Do you want to keep the existing user profile on the PC and change the Microsoft account used on that profile, or do you want to create a completely new user profile on the PC?
1
If you want to keep the existing user profile and just switch the Microsoft account.
Open the Settings App.
Go to Accounts - Your Info.
On that window, you should see either the option to 'Switch to a local account' or the option to 'Stop automatically logging into apps with this account'
Select whichever of those two options exist, that will switch the user profile to a Local Account.
Then, you can add the details of your new Microsoft account.
2
If you want to create a completely new user profile on the PC.
First, backup your files to avoid data loss.
Open the Settings App
Go to Accounts - Other Users
Click 'Add Account'
Follow the prompts to create a new account
Close the settings app
Log out of the existing user account
Log into your new account
Click the Start Button, type netplwiz and hit Enter
In the resulting dialog, select the old account and click 'Remove'
That's It, your new Admin Account will replace the old account.