I want to change your password, but don't know how to change, hope to get guidance

Hey Thesliencemen, if you mean that you want to change your login password, you can go here:

http://pbe.account.leagueoflegends.com/

Log in (upper right corner) and then click on your summoner name to be able to access the change password function.

Since you're already here, how do I agree to the summoner's code?
I try pressing the submit button, but only a red bar appears.
The only other button is cancel.
And I did try reading the whole agreement.

I think you already did?

Otherwise your post would have been grayed out and there wouldn't be a green check mark underneath your "senior member" profile.