The usual process would be to tick each one individually then click archive. The method below allows you to bypass the need to select each individual event.
- Go to Event > Manage Event >
- Open the developer console using F12
- Go to console
- Type $('input[type="checkbox"]').attr('checked','checked'); then select enter.
This will select all the check boxes on the page.
Be aware this code will tick all check boxes on the page, if you have ones that don't require checking you can't use this java script. If you only have a few to unchecked it might still be a quicker process.