I have trees on several sites since I'm able to get different information from each one, and my MyHeritage tree has lots of information that Ancestry doesn't have. I exported a gedcom file from MyHeritage with no problem. I did the research, so I trust the information in the file. It's a lot, so entering it manually would probably take a long time. I was able to import the file and compare it with my tree on FamilySearch, but I can't seem to find a way to do that on Ancestry. I looked around and did find a way to upload a gedcom, but it look like it creates a new tree, which isn't what I want. Is there a way to import the gedcom file from MyHeritage into my existing tree on Ancestry?
After reviewing my options, I decided to import GEDCOMs from the other sites I use into FamilySearch. This has the advantage of helping me get all data into one place, although it's frustrating that I can't download my tree from there once the process is finished. I'll probably import it into Ancestry as a new tree and delete my old one when I get to that point. I'm glad FamilySearch integrates with Ancestry. I checked out the question mentioned in the comments, but none of the options there worked for me for several reasons. First, I use Windows 10, and many of them were for Mac or Linux. I did try GenMerge and Twile, but I ended up giving up after a while because of accessibility problems. I'm blind and use software on my computer that reads what's on the screen, and GenMerge uses an older version of Java that's not designed to be accessible. I got somewhat further with Twile, but it was layed out so visually that it was hard to get things done. I couldn't find any other free options, so that's why I'm doing it in FamilySearch. I hope they add the ability to download your data one day.