When displaying the Group ("This assumes you really mean category") right click on the tab Group name and choose delete.
If you mean Group chat try this command in that chat:
06-07-2011 13:38 - edited 06-07-2011 13:39
There is no option to delete a group chat but you can leave it and and so can everyone else in it.
To leave a chat simply type /leave into the chat and send the message.
You can use various commands to control members in the chat, secure the chat with a password and do other administrative tasks. More here: https://support.skype.com/en/faq/FA10858
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just to add up, it also appears that the users you added will not receive any notification that they have been added to that group chat, they will only become aware of it once any user in that group enter a message. but just to be sure, you can also choose to remove the users you added in that group chat before leaving it.
I do not see the word delete when I right click or anywhere else. When someone sends me a friends request, that request should pop up in front of me to either accept or decline, but it is hidden instead. Now I read that in order to make group video calls, at least one person must have a premium account? I really hate greedy corporate America.