For example, on a previous install I installed files aaa.txt, bbb.txt & ccc.txt.
On my update I no longer want aaa.txt & bbb.txt but want ccc.tct and a new file ddd.txt.

I thought specifying '*.txt' in 'extensions to delete on clean' would do this - but reading the help it looks as if it does something different.

How can I make sure old files that are no longer required are deleted?