You can change the spacing in cells by clicking and dragging in between the cells to change their spacing. If you want to do this automatically rather than manually, click format then to cell spacing. You can select multiple cells and change their spacing all together to create a uniform look.
If you are talking about leading and traililng spaces, just use the TRIM(A1) function. To get rid of spaces betweens words or characters you have to use something like:
A1 is the cell containing your text.
CHAR(32) is the Ascii code for the space which gets replaced by nothing.