Deleting accounts is permanent and cannot be undone. This option will erase all the account progress and personal data related to the user including the following: username, team name, profile picture, biography, league wall comments, forum posts and forum comments. You can access this option clicking your profile picture in the top right corner > Settings > Privacy > Delete my account.
Once you click the button you will find a confirmation popup in which you've to enter "54321". After this your account will enter in a "grace period" of 7 days.
Resetting accounts is not an option in iGP Manager. You can delete your account so you may start with a fresh account.