how do i switch apple accounts on my iphone

Depends on what you want to switch the account for.

Your Apple ID is used for 4 different services on your iPhone. iTunes & App Stores, iCloud, Messages and Facetime.

you can sign out of each service and sign in with another account in Settings->iTunes & App Stores->Apple ID , Settings->Messages->Send & Receive->Apple ID, Settings->Facetime->Apple ID.

For iCloud, Settings->Account(top of settings)->Sign Out (scroll to the bottom).

Then sign in with the new Apple Id you want to use.

Do note, that purchased content from the iTunes & App Stores will remain tied to the Apple Id that bought it, and in the case of apps, they will forever require the original Apple ID to update.

Also note that downloading past content from the new Apple ID will lock the previous one out of the iPhone for 90 days.

See here for more details: Sign in with your Apple ID - Apple Support