Step 1
Open your main phpMyAdmin page.
If phpMyAdmin is installed by me, then it will be propably pma.<your domain>
page.
Authenticate yourself with your MySQL root
credentials.
Step 2
Switch to the «User accounts» tab using the top menu.
Locate your username in the «User accounts overview» table, and click the «Edit priveleges» link in the corresponding row:
Step 3
Switch to the «Change password» sub-tab using the top menu.
Enter your new password twice, and then press the «Go» button.