How to change passcode remotely

Please help me . I need to change the passcode on my sons ipad. It got into the wrong hands and I need either to change the passcode to get into this iPad remotely or I need to get rid of everything on this iPad. I have a feeling it's never going online until court . So please tell me how to either change the passcode remotely from my iCloud or my iPhone 6s I am the administrator of this account . I thought I set up iMessage so me and my son can send messages back and forth and I could not figure it out . In fact my personal text messages were showing up And none of my ex husbands business