Click here to see how to 'Create an Apple ID' = create an Apple Account. --> https://support.apple.com/HT204316
Merging Apple accounts (IDs) or transferring data is not officially supported, nor can it be done easily or completely. There may be some things you want to keep from the old account such as photos, some contacts, etc. Fortunately when you sign out of one ID and sign in with a different one it asks you in most cases if you wish to retain the data from it on your device. Say yes and then delete individual items you do not want.
Sign out of iCloud on your iPhone, iPad, iPod touch, Apple TV, or Mac --> https://support.apple.com/HT208242
If another Apple ID is signed in you may need to enter the password for that ID to sign out of that ID first.
Click on this link to learn how to 'Sign in with your Apple ID' --> https://support.apple.com/HT204053
Apr. 2018 post by ASC helper Winston Churchill on transferring data from one Apple ID to another. https://discussions.apple.com/message/33333380#message33333380
Feb. 2021 tips from Eric Root https://discussions.apple.com/thread/252468781?answerId=254653802022#254653802022
You cannot transfer purchases from one Apple account to another. If you are making a clean break you will just have to resubscribe and/or re-purchase items you bought through the old account. Normally Family Sharing would be a way to continue to have access but you may not want to face some of the requirements for Family Sharing.
Family Sharing - https://support.apple.com/HT201060
Set up Family Sharing - https://support.apple.com/HT201088
One important thing to do is make sure your Apple equipment is listed as being 'yours'. You do this by signing out of the Find My service with the old ID and signing in with your new one. Also make sure you take with you any receipt for the purchase of equipment.
Turn off Find My on your iPhone, iPad or iPod touch
https://support.apple.com/HT211149
How to turn off Find My iPhone on your iPhone
1. Open Settings.
2. Tap [your name] > Find My.
3. Tap Find My iPhone, then tap to turn it off.*
4. Enter your Apple ID password.
5. Tap Turn Off.
There are slight differences in the menu listing depending upon which iOS version you are using.
Set up Find My on your iPhone, iPad, iPod touch, or Mac -->https://support.apple.com/HT210400
Open the Settings app.
Tap your name, then tap Find My.
If you want friends and family to know where you are, turn on Share My Location.
Tap Find My [device], then turn on Find My [device].
Set up Find My iPhone in iOS 12 or earlier' --> https://support.apple.com/HT205362
- Home screen > Settings > [your Apple ID] > iCloud > Find My > turn on/off
- Has to be done on the device or computer itself.