If you want to close a Mint account, you can do that in the Account Settings.
We will show you below how we deleted our profile on a desktop computer:
1 Go to Mint.com and login to your account
2 Select Profile in the upper menu
3 Yes, delete my account
is a link you will find and the bottom of the Profile page.
4 Enter your password and finish
5 Indicate that you’re sure
Your account has successfully been deleted. You can now Log out.
Source screenshots (& thanks to): mint.com