This is OP, but registered on Android Central now.
@hallux, do you have any recommendations for third party ROMs? I'm checking out a quick intro
here but actual human advice is unbeatable.
Welcome to the forums. We are mostly a community of enthusiasts and don't really get into the development side of things. I'm with Hallux that the
XDA forums are going to be your best bet. They focus more on this sort of stuff, but even that may be a stretch in your case.
Custom ROM's are usually limited to popular flagship phones to make it worth the developer's time. The article you linked to is mostly just an intro to the idea. What you need is to search for a ROM that is specific to your exact model number. According to
GSM Arena, there's 5 different versions of the Galaxy Grand Prime, none of which match your model number. So there's at least 6 variants of the phone, and all 6 will have slightly different versions of Android.
So if you do decide to explore this, only use ROMs specific to your model number. Using the wrong Galaxy Grand Prime variant ROM could cause problems, up to and including bricking the phone. So while you're at it, it's a good idea to research how to recover from a hard brick and re-flash the stock ROM (and make sure you have a copy of it available ahead of time so you aren't caught off guard and wondering if it still exists).
But again, that's assuming a ROM exists for your phone. Personally, I don't think it's worth it in your case. That phone is ancient in terms of specs, and any upgrade you may find for it is still going to leave you with ancient specs and an outdated OS. Phones aren't like Widows, where you get updates for a decade and the hardware must be tailored to the OS to remain modular. With Android, it's reversed. The OS is tailored to the hardware, which gives it a much lower usable lifespan due to how fast things advance and need updated.