2 options:
1. In AMP Setup, look at the "Radius/ARM/IDS Events" and set that to 1. Wait 1 day and you will have just a days worth of events.
2. In RAPIDS --> IDS Events, there is a small downward pointing arrow icon next to "1-20" at the top/bottom left of the table. Click on it and choose another number or custom and enter in the total number of events. Then, tick "select all" at the bottom and hit delete.