You cannot make your @icloud.com or @me.com the login address to replace a non-Apple address. You can change the GMail address to something else as long as it's not an Apple address. If you are going to do this you need to follow the procedure here:
Firstly, if you have 'Find My iPhone/iPad/iMac' enabled on any of your devices, turn it off.
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).
Go to http://appleid.apple.com and click 'Manage your Apple ID'. Sign in with the current ID.
Where it says 'Apple ID and primary email address' and gives your current ID email address, click 'edit'.
Enter your new address and click 'Save changes'.
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).
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.