Can I change my username? Username vs Displayname | Beginner questions

Hi guys,

so when I first set up my username I didn't give it much thought since I just wanted to take a look at what steem.it is. Now I've decided I want to change my name but can't figure it out.

And what is the exact difference between username and display name? What name do you guys see here? (as the author)

Any help would be appreciated!

and is there a section for basic questions like these?

Greetings from Germany,

cx