1) Login to your CPanel and go to phpMyAdmin (click on it's icon).
2) In phpMyAdmin, click on your Dolphin's database name to select it. You will see the tables getting listed.
3) Click on the "SQL" tab on the top.
4) Paste the the following 2 lines in the "Run SQL query" field and click on "Go" button:
TRUNCATE TABLE `Admins`;
INSERT INTO `Admins` VALUES ( 'admin', md5('dolphin'));
5) Now, you will be able to login to your Dolphin admin with username "admin" and password "dolphin".