S3 Mini weird lags + Question about updating [CM12Lollipop]

[Sonny101]

When I play games or even search the internet or browse Google Play, the screen weirdly lags, but only the right half of it (or bottom)...it's like it is not fast enough to show me what it should and it really destroys the feel of playing. Everything (except text games) is unplayable. Also I noticed some games crash on start. I have played those games on Cyanogenmod 4.4.4 but they were running greatly, and here they just crash...and the worse part is, I have bought them and now I can't play them.

And now the question about updating:
How do I update? Do I have to download it from your site everytime and install it via TWRP or can I just download it from settings > updates? Also, I noticed that in the settings, it shows me NIGHTLY and GOLDEN. I have no idea why it is there, I have installed Lollipop yesterday and it should be a stable update.

[Sonny101]

The lags are like when you have turned off your V-Sync in a PC game...just here it is worse