You Cannot delete your messages from Schoop as they are not stored on your device.
Only the administrator can do that.
Alert messages will eventually just drop out and the device will only hold up to 30 last alerts.
The numbers for the the Android APP are below
The Android APP is around 13.70MB and then about 2.2MB data. These may vary slightly depending what version you have.
The Numbers for other APPs are below
Facebook is 250Mb
WhatsApp APP size 50.38MB then you'll have your messages on top
Hope that helps