how to change the microsoft account my new laptop is associated with

Hello,

Did they give you the password for this Microsoft account they created for the set up purpose? If so, this is what you can do:

Go to Settings > Accounts > Your info

Click on Sign in with local user instead. follow the steps and finish the rest.

(If you don't see the "sign in with a local account instead option, click on "Stop signing into Microsoft apps automatically" first, then relaunch this page. )

Restart the computer (Do Not skip)

Go to Settings > Accounts > Your info

Click on Sign in with Microsoft account instead. follow the steps and finish the rest. This time you can log into your prefered Microsoft account.

Restart the computer (Do Not skip)

Also, since the computer is setup for you with a placeholder account you don't plan on using down the road, it is important to disable bitlocker just in case you get locked out in the future and no longer have access to the placeholder account to get the key.

You can type cmd in the search on the taskbar, make sure you use "run as administrator" to launch Command Prompt, then run this command:

manage-bde -off C:

Let it run through. When it is done, the command prompt will return to the new row. Then you can run this command to verify status:

manage-bde -status