Change the value of the field level in the table qa_users for the user in question. For example, the following SQL statement will grant admin privileges to the user with the ID 42:
UPDATE qa_users SET level=100 WHERE userid=42;
Adjust privilege level and user ID as needed.
Alternatively you could change the level by username instead of by user ID like this:
UPDATE qa_users SET level=100 WHERE handle='someusers';
However, the username may not be unique, so I wouldn't recommend doing that as you might inadvertently grant somebody else elevated privileges.
The privilege levels are defined in the file qa-include/app/users.php in your Q2A application directory. Admin level is 100, moderator level is 80.