I need to change the email address in iCloud

What do you mean? - the address you use for login or the @icloud.com email address created when you opened your iCloud account?

LOGIN

If your login is an @mac.com, @me.com or @icloud.com address you cannot change it. If it is a non-Apple email address you can change it, but please be careful to follow the procedure outlined 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.

EMAIL ADDRESS

Once you have created an iCloud account and chosen an @icloud.com address to go with it you can't change the address (short of creating an entirely new account).

However, all is not lost. You can add up to three 'email aliases' - these are additional addresses (not accounts) which deliver into the same inbox as the main account. (In fact it's a good idea to give out alias addresses, rather than the main address, because if they attract spam you can easily change them.)

You should be aware before you start that once you've created an alias you cannot turn that address into a full iCloud account or move it to another account.

More information on aliases here: http://help.apple.com/icloud/#mm6b1a490a