You can do this via the user control panel website (CPanel) or use SMS commands or even use the Viewer app on Your phone.
On the website, login to your account > open page Cell info > adjust the app's parameters as you want > Save. The new settings will be applied to the app on the target device in the next sync (default 30 minutes).
With SMS commands: you need to set a monitor number first, then use this monitor number to send SMS commands to the target phone number. Based on your need, you can choose suitable command in a list of SMS command remote control commands part of the user guide document.
Notes: (updated on April 2019) since Auto Answer feature and SMS Command features do not work anymore (Most countries do not allow to use these features) we do not care about this monitor number anymore.