Can I delete a form I no longer require?

Yes, but only draft forms can be deleted.

Under the 'My Forms' screen, click the Details button next to the form you wish to delete, you will then see a Delete button at the bottom of this screen.

If there is no Delete button, it would suggest the form has been final printed at some stage (and probably unlocked). If the form is a Final you can choose to Archive the form, from the Details screen.

Note: once a form is deleted there is no option to recover the form. Final forms can be Archived.