To delete brushes is a really easy thing to do. Im not sure if you do it the same on all versions of Paint Shop Pro, but this is the way you do it in PSP 8

1. Click the brush tool looking like this

2. After that click the place I've marked on the picture below, on the brush toolbar.


3. On the new "window" that popped-up you see a trashcan. Click it ... And you will get the choose " Are you sure you want to delete this brush tip? ". If you click YES there, the brush will be deleted.