Having a hard time understanding how to actually do it? well it is simple.
Log out your game
Go to the website and log in
Go to shop and press Level.
choose your character you want to level up
It says View Info/Update BD so click Submit
You will see all info about your character
Choose your character again (If you have more than one on the account)
Click on View Info/Update DB
Choose how many levels you want to level up.
Click Submit and you're done.
Another simple and easy guide by M