Replace should remove spaces - highlight your cells then CTRL-H. In the
"Find What" panel enter a single space, in the "Replace With" panel
leave this empty, then click Replace All and your spaces should have
gone.

If you have spaces after a number in a cell (and therefore the cell
contains text), you can convert it to a number in another cell by means
of:

=VALUE(A1)

and copy this down if necessary.

Hope this helps.

Pete