Normally you will change the password by getting it into control panel . There you can change the password if you knows the old password .
Here we can change password if you forget the old password .
If you forget password either Admin account or standard account .Just login to any one account that you know the password not guest.
step 1: Type cmd in your search box . Then right click and choose run as Administrator .
step 2: Click yes.
check in the top of command prompt that now you are in this Admin (Administrator:c:\windows\system32\cmd.exe) directory.
step 3: Then there you type net user user_name 123 .
eg: net user Administrator 123. This one is for admin account . you can do this when you are in another account also. If you want to do this for another account use that user name .
now your password is 123.