I have forum like this one need some help with a query.

I have been using username1 for my admin name on my forum. Now I want to change my username to say username2. By doing this I need to run a query in phpmyadmin to update a table called post and a table called thread. I need to run a query on both tables that will change username1 to username2. Any ideas on this query.

Tables called
post fields in post table is called username and thread posterusername and lastposter

both have a userid in the table and for this user name it is userid7

Hope this makes sense.