Drop pumping sessions one at a time until you are down to two sessions that are about 12 hours apart (e.g., 6am and 6pm). Only make changes to the session you're dropping.
As you drop sessions, re-space your remaining sessions. If you are pumping at:
6am, 11am, 4pm, 10pm
When you drop to three sessions, re-space to:
6am, 2pm, 10pm