Internal Storage Problem on Samsung Galaxy Prevail?

My husband has a Samsung Galaxy Prevail that he just got from a friend who purchased a new phone. This is his first Android, so he barely does anything with it. All of the old apps that his friend downloaded were deleted before he got the phone, and he’s only downloaded a few of his own:

-iHeartRadio
-A task killer app
-A battery saving app
-Modern War

He got a warning message stating his internal storage is low. I deleted a couple of apps that he didn’t need (not listed above) and he only has 33MB of space open. He has plenty of SD card space, it’s just the internal storage. I noticed that Modern War was taking up 33MB on its own, by far the biggest space stealer. So, I moved it to the SD card. That’s when something strange happened.

The app moved fine. It now says it’s on the SD card. The storage for the app somehow went from 33MB to 9MB. No clue how that even happened. HOWEVER, the internal storage didn’t change – he still only has 33MB open.

I’m generally tech savvy, but this smartphone stuff just confuses me. So, if someone could explain this to me as if I was either a 5 year old or an 80 year old who’s never seen a smartphone, that’d be awesome.

The reviews for the phone state that internal storage is an issue, but he barely has any apps at all. Is there a way, other than rooting the phone, that might free up some space until he can afford a new phone?