No need to delete the unused fast passes .. it is actually a GOOD thing that you have unused fast passes.
What I found on my last visit:
I had three fast passes at DHS .. the first fast pass (Disney Junior) wasn't needed it was so early we just walked in the standby line and never scanned our FP and the theater was like 1/4 full.
I tried to get a 4th fast pass later at a kiosk, but it wouldn't let me. What I discovered is that my Disney Junior fast pass was unused, so it would let me just "reassign" that unused FP to whatever I want. I didn't even have to be at a kiosk to do that ... so I basically got a "free" 4th fast pass that I could easily manipulate from my phone rather than going to a kiosk. So the rest of the day I was able to toy with that Fast Pass to see what was available later. I just used it to sign up for Fantasmic .. and then later the day switched it over to Rock-N-Roller Coaster when we decided we weren't going to Fantasmic (there was FP availability 5 minutes from when I was checking at 7:35 at night).
So .. if you have early Fast Passes that aren't needed .. just go through the standby line and don't scan your bracelet and immediately reassign them via your app. Much easier than standing in line at a Kiosk.
As for Kiosks .. I only use them to get a 4th fast pass if I happen to be NEAR one .. I sometimes plan my fast passes around ending up NEAR one(so I can easily snag one during a bathroom break).
DHS is such a small park you are pretty much always near one. MK simply doesn't have enough for the size of the park (and amount of people) (They really need to put the ones back in Storybook Circus)
I've found the one at Guest Relations in Town Square to be the shortest line, but only use that if I am heading out of the park for a midday break (or back in later in the afternoon.
I don't carry a phone so we went to a kiosk and nothing would work. I couldn't do a thing with anything and guest services just deleted all three FP+. According to the CM, the system showed that all three were never used (incorrect) so the system wasn't letting us move forward.
