I looked for instructions for downloading a gedcom from Ancestry. Apparently the only option is to download the whole file. The instructions say you will usually get all the sources and notes. You will not get any images: this is because a gedcom is a text file.
You will need to upload the gedcom into a genealogy program, and split the gedcom from there. That means you will export your file as a series of gedcoms from there. For example starting with a grandparent, you would theoretically get only a quarter of your file, since you have four grandparents. If that is still too big, then start with a great grandparent, and you will theoretically get 1/8 of your original file.
Then you go through the process to upload these gedcoms one at a time.
Plan on a lot of work.
Note Kathie’s answer. She gives some good advice.