Since quite some time, my wife’s Samsung Galaxy Grand Prime (quite a mouthful, that) phone downloaded an upgrade from Android 4.4.4 to Android 5.0.2. I had been delaying the upgrade due to multiple reasons. Initially, I did not download the upgrade and kept differing. Then, one day, when the phone was connected to home WiFi, it went ahead and download the 500MB upgrade package. Even then I kept differing.
Finally, a couple of days earlier, I decided to plunge and complete the upgrade. The upgrade itself was very smooth and without hiccups.
I had been differing the upgrade due to space availability on the phone. The upgrade wanted 3GB free space on the phone and also mentioned that the available space would reduce with another GB. 1GB space on the phone is quite a premium considering it has only 8GB on board. The saving grace is the SD card, where music files can be stored, freeing up space on the phone.