1
Open the Settings App.
Go to Accounts.
Select Access Work or School, is there is a work or school Email listed there?
If there is a work or school account listed there, then they have created a group policy on your PC that requires your password to be changed to meet their security requirements and you will need to speak with their IT Administrator.
2
If there is no work or school account linked to your PC and that is your own personal PC.
Click your Start Button, then just type cmd and on the resulting list, right click Command Prompt and select 'Run as Administrator'.
Paste this into Command Prompt and press Enter.
net accounts /maxpwage:unlimited
When that command completes, close Command Prompt, that will stop your password expiring.