It's not clear whether you have two separate Apple IDs, one for iTunes and one for iCloud, or whether it's one ID with the Hotmail address as the login and the @icloud.com address as part of it.
If it's two separate IDs, you can sign out of iTunes and sign back in with the other ID, but you cannot transfer purchases from one ID to another, so it's not a practicable thing to do. You can change the Hotmail address for another non-Apple address which isn't associated with another Apple ID at http://appleid.apple.com
If it's the one ID you can't make the @icloud.com address the ID login, you can only change Hotmail address to another non-Apple one. In this cases that won't affect the iTunes purchases but you will have to sign out and back in again. However it will affect iCloud so you need to follow this procedure:
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.