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 your IOS device are below
Schoop APP is around 5.6MB with about 2MB of Data. These may vary slightly depending what version you have.
The Numbers for other APPs
Twitter is: 105MB, Facebook is 325MB, Whatsapp is 103MB,
Hope this helps