How to change performance settings?

My game gets lag sometimes and i want to lower game settings to make it run smoother, how can I change them?

Go to your options, video options, and turn everything down.

Press escape, options, and change the awesome level and resolution. Awesome level and resolution are the only two things that really matter when it comes to performance.

where is the options menu? can i change it ingame or do I have to change from my computers graphic settings?