How you can spend your work study depends if your tuition is already covered or not. If your tuition is covered by grants and aid then your work study will be used for anything else not covered (personal, books, etc) But if your tuition is not covered obviously you need to find a way to pay that tuition. One way is by you working.
Don’t fixate on the W/S. Look at all your costs. Then look at sources of funds.