Can't modify content on Skin Templates page

I'm trying to update the template file itself. I can't seem to figure out how to replace the existing file, or delete the existing file (so I can upload a new one), or modify the properties of the existing file in any way. I don't seem to have permission to make changes to anything I created in the Skin Templates folder. If I create a sub-folder, I can do whatever I wish within that folder, but I can't delete the sub-folder I created (if I wanted to). It appears to be a permissions issue, but I'm not sure if this was an oversight, or if it's was intentionally set up this way.

Two things involved here:

1. File objects and Image objects tend to get linked to their raw form -- i.e. a file Foo.zip, when listed in a folder, will get referenced with a URL that ends with '/Foo.zip', and thus clicking on it will cause the browser to attempt to download the file.  That's nice and convenient and precisely what you expect the vast majority of the time.  Except for when you're instead interested in seeing that object's '/view' or '/edit' page.  So, it's not that you can't edit an existing file object that you created, it's just that the site defers to the most common usage pattern which is that people want to download files when they click on them.  But you can always add '/view' or '/edit' to the URL of a file or image object on the site (and obviously they won't do anything if you don't in fact have permission to access the view or edit templates for the object in question.  A future update to the site will smooth this out a bit by changing the link behavior when you're viewing the 'contents' template.  So normal file & image references will continue to be of the immediate-download variety, but if you're looking at the contents tab, that tends to correspond with having additional privileges for that context, and the references to files and images will instead use '/view' so you have relatively easy access to the additional actions available from that template.
2. The 'delete' action was in fact being guarded by a test for additional permissions on the *parent* folder for the object you might want to delete.  It was intended to merely check for the 'delete' permission on just the object itself, and that's how it should behave for you now.

So - combining those two.... if you want to delete an object that you've created, just use it's normal view (adding '/view' if need be for raw files or images) and the 'delete' option will be listed in the actions dropdown menu.