Can I manually clear space that I've used with my forms?

If you are referring to 5 forms limit, then yes, you can simply  delete the form and then can create another form maintaining the limit of 5 forms in a free account.

If you are referring to Submissions then, receive 100 submission per month, as a Free Plan subscriber. If you reach the limit, your forms will be disabled and you need to wait for the counter to reset back to zero. The counter resets back to 0 every 1st day of the month.

Alternatively you can upgrade your account to any of the plans specified at pricing page to enjoy continuous service.

Let us know if you have more question