If you don't know the screen password, the only way to remove it is to reset your phone. To do that, you will need to shut down your phone and wait for about 10 seconds. After that, press and hold the Volume down + Power key combination for 10-20 seconds. Wait until the fastboot mode appears and select Hard reset. Reboot your phone, and after the resetting process is finished, the screen password will be gone.
In case you know the password, go to Phone Settings > Location and security > Set screen lock and deactivate the password directly from here.