After uploading your GEDCOM, go to your navigation home page: http://www.wikitree.com/wiki/Special:Home
. Click on the link for your "Watchlist Activity" where you will be able to see all of the profiles which were created by your GEDCOM. Choose a profile for one of your grandfather's immediate relatives. Click on the "Edit profile" tab. From there, you can connect this person to your grandfather by choosing to add a parent, child, or sibling, depending on your grandfather's relation to them. At the top of the new profile page, there is a prompt asking if the person you would like to add already has a WikiTree ID, and this is where you put in your grandfather's WikiTree ID. Save the profile, and your grandpa is connected to the people in the GEDCOM. Hope this helps!