This is only possible on the mobile app right now.
- Using the mobile app, select your league
- Press the League Settings icon at the top.
- Scroll to the Commissioner Control section and select "Edit Roster FAAB" or "Edit Roster Waiver Position"
- Make edits and then press "Save"
There you go! All waiver budgets and waiver positions updated in one shot!
... remember: with great power comes great responsibility.