go to ALL ITEMS then check COLLECTIONS Double Tap Each one... when they are DL they will have a STAR next to them. Any You don't want either leave in Cloud or hold your finger on & then when the choices pop up just tap Delete from Cloud
I buy 90% of my ebooks from Amazon BUT download ZERO to my PW4 I HATE the way Authors feel they need to Repeat the title 2-4 times & you cant tell which # in the series is! I also convert everything for my Kobos