change svn:externals property in subclipse

I thought this would be simple, but for my life, I can't change the svn:externals property in subclipse! I have it set to:

wp http://core.svn.wordpress.org/branches/3.0

And would like to set it to:

wp htt开发者_StackOverflowp://core.svn.wordpress.org/branches/3.1

If I go to the 'team->set property' dialog, it says "Another property has the same name" and it won't let me change it.

what can I do? thanks for your help!

"Right-click > Team > Show Properties" You can edit them in the "SVN Properties" View.