If you are trying to switch accounts on the phone... There are two different ways.
Hard reset or factory reset and use the new account during setup. Settings > about > reset your phone. You will loose all backups, data saved to the cloud, access to old OneDrive docs and pics, App ownership etc. from the old account. The new account starts with a clean slate and you can not transfer anything over from the old.
If you want to shift the current account to a new email address for the primary... It gets a bit long and complex. Sign into your Microsoft Account on your PC browser. Add the new email address. Make it Primary. Wait about 24 hours and delete the old email address. It takes about 48 hours for the changes to hit all the Microsoft servers and to show everywhere. You do not loose any data, App history or privileges from the account. Even my Microsoft Gift card balance transferred when I did this. One glitch I had was my Skype won't let me switch emails it reports too as it won't take the new password. Another user said they had a problem merging xBox Gamer Tags. Any inconveniences would most likely be minor. A call to Microsoft Customer Care should get that sorted. I've been a bit lazy on follow through for my Skype issue...