my icloud mail

Evidently you want to change your Apple ID which forms the login for your iCloud account (not the @icloud.com which the account provides and which you can't change). Please follow these instructions carefully to avoid problems:

If your primary address (the ID) is an @icloud.com, @me.com or @mac.com address you cannot change it. If it is a non-Apple address you can change it as follows:

1. Firstly, if you have 'Find My iPhone/iPad/iMac' enabled on any of your devices, turn it off.
2. Create a new email address, for example at Yahoo or Gmail, or anywhere convenient (or you can use an existing address as long as it has never been associated with an Apple ID).
3. Go to http://appleid.apple.com and click 'Manage your Apple ID'. Sign in with the current ID.
4. Where it says 'Apple ID and primary email address' and gives your current ID email address, click 'edit'.
5. Enter your new address and click 'Save changes'.
6. Now you will need to go to each of your devices and sign out in System Preferences (or Settings)>iCloud - 'Sign out' on a Mac, 'Delete this account' on an iOS device (this will not delete the account from the server).
7. Then sign back in with your new ID. Your iCloud data will disappear from your devices when you sign out, but reappear when you sign back in.

I re-iterate: before you start, turn off 'Find My Mac' (or whatever) or you will need the services of Support.