phpMyAdmin-#1142-UPDATE command denied to user 'MyAccount'@'localhost' for table ...

[Comunitaro]

I'm trying to run a simple SQL script from the phpMyAdmin tool. I haven't used phpMyAdmin a lot and I couldn't find a way to change the user that I am logged in from default user 'MySiteGroundAccount'@'localhost' to a MySQL account that I created and configured. Every time I run a SQL script or I try to import a SQL script as simple as the one below, I get the error that you see. Any ideas how I can login as a different user using phpMyAdmin or what I can do to fix this?

Error
SQL query:

UPDATE MyDBName.phpbb_users SET user_regdate = UNIX_TIMESTAMP( "2004-01-25 00:05:04" ) ,
user_posts = '4',
user_from = '',
user_website = '',
user_occ = '',
user_interests = '' WHERE username = 'SomeUser';

MySQL said:

#1142 - UPDATE command denied to user 'MySiteGroundAccount'@'localhost' for table 'phpbb_users'

[Comunitaro]

Removing the database name (like below) from the script fixes the problem.

UPDATE phpbb_users SET user_regdate = UNIX_TIMESTAMP( "2004-01-25 00:05:04" ) ,
user_posts = '4',
user_from = '',
user_website = '',
user_occ = '',
user_interests = '' WHERE username = 'SomeUser';