how to delete multiple ogv and webm files

There's no method, using DW's Find & Replace tool, to search by file type and make a selection to delete a given file type from your site entirely, but you can still use DW to clean up your server files...

1. Click the Connect button (plug-in icon) in the Files Window
2. Click the Expand button (two square icon) in the Files Window
3. Right Click on the bar, just above your Remote Root folder name, and to the right of "Remote Server"
4. From the drop down menu that appears, choose "Type"
5. Open all of your folders by clicking the small arrows to the left of their names
6. Click the "Type" column header to sort them by extension

This will group the files by type for each folder. You can then go through and select them by Shift+Click and Ctrl+Clicking to highlight, then delete.