How do i delete past events?
Unfortunately you can't delete the event if it has participant. If you delete them the its participants will be deleted automatically. Even its not advisable to delete price set if it was ever used to record participant ticket, contribution or membership. If you delete them you will loose all financial data associated with it or the system might behave weirdly if you ever try to update the participant or contribution or membership.

If you want this price set not to be displayed on screen then you can set is_quick_config = 1(TRUE/Yes) either running sql or from api explorer.

Cheers

Pradeep