I'd imagine that 4GB is plenty of RAM if all you're doing is web browsing. That doesn't really seem like the problem to me. It may be your display drivers that are out of date, although I have no idea how to update them on a Mac. I'm sure if you Google it, it'll probably tell you, though.

It's probably not related to your hardware. You could try updating or reinstalling your browser - not sure how to do that with a Mac. But those specs are plenty for web browsing.
Many older browsers get stuck in modern JavaScript. Also, security settings can be an issue.

I come from a PC background rather than Mac. I always advise that more ram is the most cost effective upgrade you can give a machine. After that I'd assume that a 2011 laptop is likely to have a spinning disk style hard drive. If so then look to see if an upgade to SSD is possible.

However that's about improving performance. Simple lack of performance does not explain freezes and lack of images for basic web browsing. For that I'd suggest the there's an underlying problem that better hardware will only fix if the underlying problem happens to be faulty hardware.

Formatting the hard drive and reloading the Operating system from scratch is a rather drastic move if you don't know for certain that it's a software problem.

I'd suggest that instead you prepare a USB drive and boot from that.
Here's some MAC centric instructions I found for setting up a Ubuntu on a USB stick
Once you're able to boot from a USB stick you can see if you still get the problems. If you do then you're eliminated the software as the cause of your problems and you can move onto running hardware diagnotics.

If not then a fresh install can work wonders - just don't forget to back up your data first.