Are you using the Online browser version? It doesn't have the Forms Mode.
To compare Joint to MFS. If you are using the Online version, do NOT change anything on your return. You would have to start with a new account and do a test return. You don't have to pay unless you want to print it out. So you might need 3 accounts, one for Joint and two MFS, one for each spouse.
It would be better to use the Desktop CD/Download program. It can do unlimited returns and has a What If worksheet to compare them and many other advantages over the online version. You can move your current online return to the Desktop program without paying for Online.
If you have the Desktop program for Windows the Forms button is in the upper right. For Mac I think you go up to menu item View - Forms.
