First, perform an extended power cycle, 10+ minutes, fully powering down the unit. Steps on how to do so safely can be found here:
You can also clean the touchscreen using the clean function. Finger oils, prints, dirt, etc. will buildup over time causing the screen to be imprecise. Navigate to Settings > Clean Screen. This will give you 30 seconds to wipe it down with a microfiber cloth and the screen will become inactive.
After following the above steps, arm/disarm the system. Any change?