1. If both are in same college:

you need to contact your International Office and  they will guide you how to do (What form to fill up, How much it cost etc). You need to apply to INS and it will take anywhere from 6-12 months. Both need to be in F1 status until spouce gets F2 approved.

2. If both are at different college:

Contact Int Office and informed them that your spouce is applying for change of status from F1 to F2. You need to apply to INS and it will take anywhere from 6-12 months. Both need to be in F1 status until spouce gets F2 approved.

3. If you have any questions or you didn't understand what your Int Office told you, post in this thread, I will help you.

Good luck.