On the website: to change your password, click on the "gear" icon in the upper right hand side of the screen that goes to "My Account". Click on the "Settings" tab and the 2nd from bottom option is change your password.
If you're using the app: to change password, click on the 3 dots in lower right hand corner for "More" menu. Tap on "My Profile" and click on "Change Password".
The Grokio team