With MIUI 7, we also got 4 new themes added to our phones.
But if you are looking to save some space, or just don’t want the default themes cluttering up your options, here’s how to delete them. 
Go to your Themes App -> Offline.
You’ll now see the 4 default MIUI 7 themes. Just hold-press the Themes you want to delete. Then choose ‘Delete’ to confirm.
All done!
