What to do to protect my Wi-Fi from iphone users?

Okay… This is the thing… Recently I gave my Wi-Fi password to my friend and he used to from his iphone… What can I do so that my friend won't get access to Wi-Fi the next time he comes to my place.
What I want to know is there anyway so that the iphone or any other device won't get access to my Wi-Fi again.

You have two options
1. Kindly ask you're friend to go to settings->Wi-Fi-> Click the arrow next to your network and click forget network
2. Change your password
Also as a side not using someone's Wi-Fi without permission is leeching, which is illegal.

Yes…
1.Go into your Router CP
2.Change password
3?
4.Profit.

Change the Wi-Fi password not rocket science.