By "add properties", do you mean add an aspect? You can add an aspect by selecting Run Action from the View Details page, select Add an aspect to item from the drop down list, and then select the aspect to add. Once you have done so, you can then Edit Details, and you will be presented with an edit form, including that for the aspect you just added.
I see. I actually wanted to add properties to the space but now see its easier to add an aspect. So I need to add the properties I'm interested in adding to an aspect and add the aspect to the content model.