How do I lock my linksys wireless connection?

I'm on a linux computer right now. Linksys router.

I live in an apartment complex and during the day my internet goes really slow and disconnects a lot. But during the middle of the night it works much better. This leads me to believe other people are using the connection and bogging it down.

I tried encrypting it before and it was a hassle so I took it off, but I can't find my thread I made before explaining how. How do you view your threads on this site? D: (not posts)