The Windows OS is full of surprises and vulnerable to hackers. It is very easy to hijack the local admin account by exploiting the a little loop hole in security. Suppose you have a limited user account on windows machine, now if you follow the below steps you will end up gaining admin access to that machine.

1- Go to the system32 folder and copy logon.scr and cmd.exe to a safe location so that they can be backed up once you are done.
2- Now delete the logon.scr file from system32.
3- Rename cmd.exe to logon.scr in the system32 folder.
4- Run logon.scr

This last step will open a command prompt with full admin access.

5- Now from the command prompt open lusrmgr.msc by typing it in.

lusrmgr is a tool to manage user.

6- You can now unlock the admin account and set a new password
7- Restore the backed files

Now you can logout and login as admin user.