To change your current password, log into your account, tap on your balance in the top right corner, and then select "My Account" from the drop-down menu.
On the next screen, go to the "Account Settings" section on the left menu. Here you will see the "Change password" section at the bottom of the screen. Enter your current password and the new password you want to use, then click "Submit". Once this is complete, the password for your account will be updated.