A few things you could try to fix the screen lag (if you got an old computer running with low specifications);
- In-game, click settings tab > Video - lower your resolution.
- Then go to - Settings > 1337 (last option) > enable Archetype (must be look like [X]).
- Update your VGA drivers.
- Close processes which you think might be causing in-game lag.
- Go in-game again and click on the settings tab > 1337 > set max FPS to 333 or 500.
