Thanks, Renato. The Oneplus Two sounds like it will be an even bigger killer, when it is announced next month. I think my phone has a good year or 2 left on it though.
I do recall having some issues with Gingerbread (2.3) with the memory issue. My Galaxy S at the time had a relatively small system block, though.
The biggest issue that I have with Lollipop (5.1.1) is whenever I do a backup (full system) overnight, it trips out the Wifi connection, and I have to manually reconnect every morning.
If you are interested in Root access, I found an easy tutorial for you:
http://playfuldroid.com/how-to-root-...-than-an-hour/
If you do this, then you can go to the Play Store and install a root app remover application, and free up some space.
**Important Disclaimer** - Whenever you do something like this, there is always the possibility that you may brick your phone. If you cannot afford to be without your phone, then it is not recommended to do. Proceeding is done at your own risk (as it is with all of us).