how can i clear all content from a database collection and upload new one quickly like a reset or select all and then delete.

In Editor mode, you go to the Database section. There you have the choice between Live and Sandbox view. If the sandbox is empty you can sync Sandbox to Live. This should empty it.

You can also simply select all records in the Content Manager and then delete them.

BEWARE: you cannot undo it.

that is the question how to empty the sandbox?

Hover over the number 1 at the left. Click it. Scroll to the last record and SHIFT click the last record.

All your records are selected. Now click delete.

ok thanks it just started to work even with ctr all (select all and delete

The click and scroll is very painful if you have lots of records - I’ve 6000.

Cmd-A doesn’t select the records in chrome on OSX.