I am having a problem in deleting entries in SAP F4 help using GuiXT. The requirement is to have only a limited number of entries available for the user. Can you please advise me how to go about it.

It is not possible to delete entries in F4 help with GuiXT.  An alternative, if there are only a few possible values, is to delete the entry field and to use a couple of radiobuttions instead; see keyword documentation on Radiobutton command.