I'll answer myself and summarize based on my findings:
> how do I delete forms while amending a return?
You cannot explicitly delete forms. The amend process does not have a "delete forms" link in tools.
(In my particular case of the form 2555 problem, I had to zero out everything in the flow related to foreign income and foreign taxes so that forms and worksheets would get automatically deleted, and then re-enter the info in these sections from scratch.)
IMPORTANT: before you enter the "amend my return" flow, download and back up the .tax and .pdf files corresponding to your originally filed return. The amend process will modify Intuit's copy of these files directly, and they won't be restored even if you cancel the amend.
