Go into Settings. Choose mail, contacts, calendars. If you do not have an iCloud mail account, set one up with your current Apple ID. If there is already an iCloud email account, delete it and create a new iCloud account with your current Apple ID. If you want to continue to receive email from your old account/ID, you can add it back in once you have created the primary account.
To set your Apple ID to your current Apple ID for iTunes and the AppStore, in settings, go to Store and change your Apple ID there.
I have the original version 1 of the iPhone so there is no way to access the cloud.
I have a MacBook Pro and an iPad, both of which are set to my current email address and password (I think).
I have gone to settings, Store, logged in to my old account and edited my email address and password however I get the message "That email address is already in use as an Apple ID".
Sorry if my question sounded terse. It was not intended that way. What I was trying to ask is whether uniformity was your only goal or if you were trying to accomplish something else like using one ID for your email, and using another for your Store account...
Since you saw the message: "That email address is already in use as an Apple ID" it is possible that you tried to create a new Apple ID instead of changing the Apple ID associated with your iPhone. Please check and see if there is another option available to switch your ID. On my iPhone you do it by tapping on the current Apple ID that is shown in Settings > Store.
One other thing. If I understand yuor post correctly,uniformity is your only reason for switching the ID on your iPhone. If you switch your Store Apple ID on your iPhone, it may make a little extra work for you when you update your apps. That is, the apps you purchased with the old ID will need your old password before they update. Then, if you purchase any new apps with your current ID, you will have to put in a passord for that ID to update those apps. Even if you use the same password for both, you will have to put in the password twice.
This is really confusing. I wish Apple would let people consolidate IDs. It would make issues like this much simpler.