questions about returning equipment

hi ... i need to return my xfinity cable tv box, the xfinity remote control, and my xfinity router/modem ... i believe that's all the xfinity equipment i rent ... i don't have a printer to print out a label ... can i just return these 3 items to any ups store and will they box stuff up for free and know where to mail the equipment ?? also, is the only cable that needs to be returned the power cable that powers the TV cable box and the modem ? i believe i provided all the other cables (like the ethernet cables) ... and is there a form UPS fills out ? how does comcast know i'm returning the equipment ...?? can they figure this out from the serial numbers ? thanks