How can I change my email?

It's not possible to change your email.

You can open a new account through your new email, but your profile history (points, levels, rank, etc) will be lost. 

Remember that there are 3 login options: Facebook, Google, and your personal email.

Each login method corresponds to a different account. 

If you have created multiple accounts via multiple methods (i.e. 1 Facebook and 1 Google), you'll have multiple different accounts.