With Mike's suggestion of merging your 4 separate projects, you could then easily export from that a new gedcom just containing your direct ancestors. If your 4 projects only have you as the common link, then merging becomes much more straightforward, and you would only merge those 4 projects (each in turn) into a
new composite project (ie. you wouldn't modify your existing projects in any way, so no danger of messing them up).
However, if you really want to keep it simple, just export an ancestor only gedcom from each of your 4 projects, then merge those into a new project, so again no danger of messing up you existing projects.
In any case, you do have backup copies of your existing projects, don't you
I'm sure that Mike can help you through each step, whichever way you choose.
David Miller - researching Miller, Hare, Walker, Bright (mostly Herts, Beds, Dorset and London)