Let's assume your current sheet is called "Sheet1". Make a new sheet
called "SheetNew" and in A1 of the new sheet, type this:

=TRIM('Sheet1'!A1)

Copy this across rows and columns on the new sheet until you have
captured all the dae from Sheet1. Then select all cells  on SheetNew, and
hit CTRL+C. With all cells still selected, go to the Insert menu, choose
Paste Special and in the dilaog, select 'Values'. Click OK.

You can now delete Sheet 1 and SheetNew contains all your data, trimmed
as required.