The compute function is found under the ....menu.
After
selecting compute a window will open up. The picture below shows
how you can add a constant (e.g., 3) to each score in a distribution
(var001).
step 1: select the distribution (the variable) that you want to
transform.
step 2: type in the transformation that you wish to use on the
distribution (in this case adding 3 to each score).
step 3: type in the name of the new variable that you are creating by
transforming the distribution (note: you are not erasing the former
distribution, but instead creating a new one, so it'll show up in a new
column).