when i go to accounts to change it, it asks for the old one in order to put a new one..so i don't know it

 

Are you using a Microsoft account or a local one?

The local account PIN can be only changed with the old one as far as I know. There's a separate reset procedure for Microsoft account, under Settings > Account > Sign-in.



Otherwise back up your important stuff and reinstall. Scratch that, back up anyway whatever you decide to do.

 

In order to remove all locally stored PINs and possibly even Finger-Prints, you must delete all contents of %windir%\ServiceProfiles\LocalService\AppData\Local\Microsoft\NGC.

The quickest way to accomplish this is using the two following commands in an elevated Command Prompt / CMD (run as administrator).

takeown /f %windir%\ServiceProfiles\LocalService\AppData\Local\Microsoft\NGC /r /d y

icacls %windir%\ServiceProfiles\LocalService\AppData\Local\Microsoft\NGC /grant administrators:F /t

The first one will take ownership of the folder, the second one then will grant administrators rights to it.

Once this is done, you need to delete all contents of the folder. If you are logged on as an administrator you can just use Windows Explorer. If you are logged on as a regular user, you need to do it either more manual in CMD or use e.g. a tool like 7-zip in elevated mode and navigate to the folder, be aware that 7-zip might not be able to handle %windir%, either navigate manually to the folder or use C:\Windows\ServiceProfiles\LocalService\AppData\Local\Microsoft\NGC to get to the path. Delete all contents.

Reboot.

Setup PIN again.
This is taken from here.

I did this few months ago.