If you want to change your password, go to Settings, which you find by clicking on your profile picture in the lower left corner in your client, and then go to General settings > Change password.

If you've forgotten your password, you simply click on Forgot your password? below the log in button in the ImBox client. As Username, you type the e-mail address that you use in ImBox. Afterwards, you get a link sent to your e-mail where you get to choose a new password.

Please note that the password you choose/have, is used in both the ImBox client and Admin.