Cannot delete i386 from external harddrive

You have to take ownership of the folder and sub objects then give yourself permissions.

Right click on the folder and select properties. Select the security tab. Click on advanced. Select the owner tab. Select edit. Select your username from the lower box and check the Replace owner on subcontainers and objects. Then click OK.

That gives you ownership.

Now select the Permissions tab. Clcik change permissions then add. Type in your username. Give yourself full permissions. Check "Replace all child object permissions..." and click OK. Now you have ownership and full permissions to delete.

I've added myself as admin, but it says
"you need permission to perform this action

You require permission from administrators to make changes to this folder"

Did you do the steps I outlined?

Here are a couple of tutorials that may help you:

http://www.vistax64.com/tutorials/67717-take-ownership-...
http://www.sevenforums.com/tutorials/129063-take-owners...[2]=Security%20System%20Tools