Use the option Export CSV in the top right corner of the All Activities page. Just keep on mind that it will only export activities loaded on that page, so you have to scroll to the very end, if you really want to export them all.
I knew that. The problem is : I would like to download ALL activities (since around 2011, average 1 activity / day). It takes ages to scroll to the very end and it stops at the middle of the Process.
