If you are trying to "unblock" a person on the list so that person can call you do the following: Open the "Skype" menu and click on "Privacy". You should see a button that says "Blocked Contacts". Click on that button and it will exposed a list of the callers you have blocked. You can delete any or all of these callers.
BTW, I know it works for Windows but I do not know if it works for Mac.
This did not work for me and I have windows 7. I have many unwanted callers blocked and I just want to get rid of them. How can these be deleted please.
Go into "Conversation", then into "blocked". You can then choose who you want blocked and have them also removed. Hope this helps. Just discovered it myself.