Yeah, this should be possible. If you go to the "My Collections" page, here: http://www.criticker.com/?cl&mine
and then selected the "Edit Collection" option under the expanded info for the collection in question. You should there see an option to change the collection's type ... Public, Private and Hidden are the options.The only exceptions to this
are the Remembered Films and Ignored Films collections, which are locked as Private Collections. These are special collections which are tied into other functionality at Criticker, so their types can't be changed.