This is quite an easy thing to do – if you know where to look. But I’ve reproduced this here – in case you dont…
Q: Do you know how to remove an Outlook form from the Exchange organizational forms library? I know how to publish a form into the Exchange Oorganisational Forms Library, but, I haven’t seen anything on how to remove an unused form from there.
A: 1. On the Tools menu, click Options.
2. Click the Other tab and then click Advanced Options.
3. Click Custom Forms and then click Manage Forms.
More info can be found