To hide a form that you no longer need, you can archive it.
If you choose to archive a form it can no longer be viewed, receive contributions, or be edited. However, you can revive the form if you need to.
After archiving a form it will turn grey (as you can see below), but it will still be listed in the same spot in your contribution list as it was before it was archived.
If necessary, just click Revive at the far right of the table and the form will become active again.