Can I update my Samsung Galaxy S4 to a newer version of Android?

I've been trying for weeks to work on this myself, but I'm stuck. I have a Samsung Galaxy S4 through StraightTalk/TracFone (Walmart). It runs on Android 4.3, and I've learned that StraightTalk does not push OTA updates to the Android system. I love the phone but the outdated Android is starting to cause problems--I have apps that I love and use every day that now are no longer working because they aren't supported.

I tried Samsung Kies and found out that doesn't work for my device. Then tried Samsung SmartSwitch, but it doesn't offer me an update. Finally I tried Odin...but when I search my model number on Sammobile, the only firmware it offers is what I already have (4.3).

Does that mean it is impossible for me to update it? Like no newer version of Android is compatible with my phone? I know the phone is old, but I like it and don't have any issues otherwise, so I'd rather not buy a new one.

Thank you!