Our memories are fickle and although you can't technically "fill up" your memory, you can definitely overload it.
Fact - we cant remember everything. So don't try to. Decide what you need to learn now, and what you can save for another time.
Here at Brian we call this "Knowledge for now : Knowledge for later"
And its a decision I make for every piece of information I come across. What do I need right away in order to meet my short term learning goal, and what do I need later, maybe when I become more proficient and want to move to the next level?
Lets say I'm learning to swim; I'm watching YouTube videos and reading hints and tips on technique. I'm only a beginner and so for now the information I really need is explaining the basics. But I have a goal, I want to be able to swim a mile. As I come across information that's currently too advanced I'll save it for later. I'll always save it in the same place - I personally like online apps like Evernote and Pocket - because then I know where it is. Im not going to clog my brain with it right now, not until I've practised what I've learnt, got the basics right in and them I'm ready for the next level.
This is the same with any information. Be organised about where you file your data and your learning. Keep it in one place so you always know where to go to when you need it.