You need to select a part to edit before it won’t be greyed out. You also need to start from a part that has the correct number of pins as parts editor can’t change the number of pins. These two tutorials will probably be helpful (old_grey’s covers parts editor, I don’t use it.)
I lately learned there aren’t links to the videos in Old_Grey’s tutorial so you need to do a google search for the title and then they come up on YouTube.