1) Go to
imgflip.com/settings
2) Make sure the email there is correct. If it is correct, hit the red button next to your email, that says something like "Send email". The verification email should arrive in your inbox nearly instantly, you may have to check your spam folder though.
3) If the email there is not correct, first enter the correct email and hit the "Update" button at the bottom of the settings page. Updating your email address should automatically generated a verification email. If not repeat step two.
I hope that helps.