Replace variable declaration 
of type X with appropriate
value from method cl_abap_char_utilities

i.e. 	CONSTANTS: 	
  con_tab TYPE x VALUE '09',
  con_cret TYPE x VALUE '0D'.
would be replaced with
CONSTANTS: 
con_tab TYPE c 
  value cl_abap_char_utilities=>HORIZONTAL_TAB,
con_cret TYPE c 
  value cl_abap_char_utilities=>CR_LF.

Upload/ws_upload and download/
ws_download are obsolete, 
since they are not Unicode enabled. Replace
with appropriate methods 
from cl_gui_frontend_services. 
Please also note that the data 
types of the various
parameters will also probably 
also need changing for the 
new method calls but the 
code below demonstrates
how to do this. I_TABLE is 
the original table and 
IT_UCTABLE is the converted table.

i.e. Function module ‘WS_DOWNLOAD’
  CALL FUNCTION 'WS_DOWNLOAD'
      EXPORTING
           FILENAME                = p_file
           FILETYPE                = 'ASC'
         MODE                    = ' '
       TABLES
            DATA_TAB                = i_table
      EXCEPTIONS
..
would be replaced with
data: gd_file type string.
types: t_uctable like line of i_table.
data:  it_uctable type standard table of t_uctable.

  gd_file = p_file.
  it_uctable[] = i_table[].
  CALL METHOD 
      cl_gui_frontend_services=>gui_download
  EXPORTING
    filename = gd_file
    filetype = 'ASC' " DAT,WK1
    Append   = ' '   
          "if mode = A then this would be X
  CHANGING
    data_tab = it_uctable
  EXCEPTIONS
    OTHERS   = 1.

Function module ‘DOWNLOAD’
      CALL FUNCTION 'DOWNLOAD'
        EXPORTING
          filename = p_file
          filetype = 'WK1'
        TABLES
          data_tab = i_table.
..
would be replaced with
data: gd_file type string.
DATA: ld_filename TYPE string,
      ld_path TYPE string,
      ld_fullpath TYPE string,
      ld_result TYPE i.
types: t_uctable like line of i_table.
data:  it_uctable type standard table of t_uctable.

  gd_file = p_file.
  shift gd_file RIGHT DELETING TRAILING '\'.
  shift gd_file RIGHT DELETING TRAILING '/'.
  shift gd_file left DELETING LEADING space.

  CALL METHOD 
       cl_gui_frontend_services=>file_save_dialog
    EXPORTING
      DEFAULT_EXTENSION = 'WK1'
      default_file_name = gd_file
      INITIAL_DIRECTORY = gd_file
    CHANGING
      filename          = ld_filename
      path              = ld_path
      fullpath          = ld_fullpath
      user_action       = ld_result.

  check ld_result eq 0.
  gd_file = ld_fullpath.

  gd_file = p_file.
  it_uctable[] = i_table[].
  CALL METHOD 
       cl_gui_frontend_services=>gui_download
  EXPORTING
    filename = gd_file
    filetype = 'ASC' " DAT,WK1
    Append   = ' ' 
          "if mode = A then this would be X
  CHANGING
    data_tab = it_uctable
  EXCEPTIONS
    OTHERS   = 1.
Or in circumstances where you need to add field 
texts to the first line of the file you could use the
GUI_DOWNLOAD function module:
DATA: BEGIN OF fields_tab OCCURS 0,
        f1(50),
      END   OF fields_tab.

fields_tab-f1 = 'field1 text'.
APPEND fields_tab.
fields_tab-f1 = 'field2 text'.
APPEND fields_tab.
fields_tab-f1 = 'field3 text'.
APPEND fields_tab.

  CALL FUNCTION 'GUI_DOWNLOAD'
    EXPORTING
      filename                = i_filename
      filetype                = 'DAT'
    IMPORTING
      filelength              = filelen
    TABLES
      data_tab                = itab
      fieldnames              = fields_tab
    EXCEPTIONS
           .....
-----
Note: ‘ws_upload’ and ‘upload’ would be the 
same as above but would use the
cl_gui_frontend_services=>gui_upload 
method call instead:
 CALL METHOD 
        cl_gui_frontend_services=>gui_upload
  EXPORTING
    filename = gd_file
    filetype = 'ASC' " DAT,WK1
    Append   = ' '
  CHANGING
    data_tab = it_uctable
  EXCEPTIONS
    OTHERS   = 1.

Add ‘ENCODING’ addition to statement

i.e. 	OPEN DATASET G_DATAFILE 
              for OUTPUT IN TEXT MODE.
would be replaced with
	OPEN DATASET G_DATAFILE 
             for OUTPUT IN TEXT MODE 
             ENCODING NON-UNICODE.

IN..Mode is expected within 
open dataset command.

i.e. 	OPEN DATASET wfilepath FOR OUTPUT.
would be replaced with
	OPEN DATASET wfilepath 
                 FOR OUTPUT IN TEXT MODE 
                 ENCODING NON-UNICODE.
Or 	OPEN DATASET wfilepath 
                 FOR OUTPUT IN BINARY MODE.

FOR INPUT, FOR OUTPUT, 
FOR APPENDING or FOR UPDATE expected!

i.e. 	OPEN DATASET wfilepath FOR OUTPUT.
would be replaced with
	OPEN FOR OUTPUT DATASET wfilepath 
                 FOR OUTPUT IN TEXT MODE.

THE DESCRIBE LENGTH can only be used 
with the IN BYTE or IN CHARACTER MODE

i.e. 	describe field e_text length line_length.
would be replaced with
	describe field e_text length line_length 
             IN CHARACTER MODE.

The statement ‘ASSIGN PATH+PATHLENGTH TO 
.’ Returns the following error message:
"You cannot use ASSIGN f+offset. 
Always use an explicit length (or '*')".

i.e. 	ASSIGN PATH+PATHLENGTH TO 
. would be replaced with
	ASSIGN PATH+PATHLENGTH(2) TO 
. “replace 2 with the length of the field

Itab/structure and “ “  are not mutually 
convertible in a Unicode program

i.e. 	G_SHOW_LIST = SPACE.
would be replaced with
	Clear: G_SHOW_LIST.
Or  	G_SHOW_LIST-field1 = space.
	G_SHOW_LIST-field2 = space.
					…etc

var and var  are not comparable 
in a Unicode program

Example 	Data: VAR like tabix.
was replaced with
		Data: VAR type sy-tabix.