I need to change my primary Apple ID and use a second one that has been used for my Apple TV and other stuff

One Apple ID account for one user should be enough for most people, as that can do all that is needed. You can’t transfer purchases or subscriptions or other services between accounts. You can’t merge accounts. You can’t re-register as first user for certain devices and promotions. It may reduce the Family Sharing group size needlessly. When you need to verify the administration, you would need to do so for each account.

That being said, you can sign out of a device and sign in again with a different account.

On some devices, you can have multiple accounts, although one of those would be active at any one time.

Historically, iCloud services have always had a separate entry, so that may or may not be a different account without much consequences.

If you describe what issue you run into, then that may help with more specific answers .

The Apple eco system is based round a SINGLE ID across all platforms .

If you have multiples , you will need to choose ONE and jettison the other .

You may loose the ability to upgrade apps and music purchased on the jettisoned account.

What you need to do is to tap settings/your name at the top of the screen of the iOS device to be deactivated, to open the ICloud manager pane.

Scroll to the bottom and tap sign out It’s in Red . You will be asked if you want save and backup some things. Decide now and then again tap and sign out.

You then have to sign in with the other accounts credentials on that same device.

You may now have to update/modify/add to a few apps certainly Mail to point at both the new account ID mailbox and also your account that you just logged out of.

Mail accepts multiple email accounts as standard .

Music,Apple TV, News and iCloud will sync with the devices on the new account.

Also Safari bookmarks will need adjusting and or to be repaired by you, because the now deactivated accounts setting and associated keychain information will have been purged.

However, what you can actually do is to make yourself a “family member”( it will cost you more in subscription charges as a result ; caveat if you do have up-to three other family members, partners, children, parents etc….. they can also be added at no extra cost)

Step ONE you need to create an email account for what will become the second or sudo “family member” device now it will be important in the following steps .

You will have created two separate email addresses automatically with one linked to each separate ID.

The way forward would be the decide which ID would be the primary one; whilst of course the other would become the secondary account Sudo”family member “

On the primary account you are going add the second ID as a “family member” and choose what to allow. Music, Apps, purchase sharing etc…… in subscription services.

On iOS devices to be the primary account tap

Settings/Your name on the top of the next screen to open the iCloud manager page.

Tap family sharing and then the + to add family member ( your other ID) and “invite people” . An email will be sent to the other (you in this case) email address which you accept/decline on the other device.

Caveat if you haven’t set up an email account for your other device YOU do have one attached to the ID automatically.

So you need to create that email account on at least one device (BEFORE THE ABOVE STEPS)

Once you have done all that the two accounts will be linked in a family group scenario.

Tick which services to share and done

A cludge and a cost to you however will work.