In case you lost your admin password and recovering it by mail does not work for any reason here is how you can solve the problem.
First you should know that the password is stored in the table users
. The actual field is pass
The password is stored in md5 format
. So what you need to do is:
1. Go to phpmyadmin or similar db management tool.
2. Open _users table
3. Locate your record (probably the first)
4. Edit the record
5. Set the password field by writing a new pw and setting the "function" to MD5
6. Log in with your new password
[original answer by mithrandir]