To upload a GEDCOM file, go to your profile (on the top right side of your screen if you're on a Desktop device). You'll see an overview of your user data and family trees, and on the bottom of the page the button "Create or import new family".
This will lead you to a fresh family tree that only consists of a person labelled "Me". If you select this person, the appearing sidebar will offer you the option "Import GEDCOM or family script" on the bottom left side. If you click on the button, you can upload any GEDCOM file you have.
Hope this helps!
