Are you talking about you GEDCOM file? If so, go to your Ancestry page and then go to the individual tree you want to export. Right under the Ancestry logo on the top left, there will be a drop down menu that says "____ Tree" with your family's name. Click on it and then click on Tree Settings. On the right hand side, there's a green button that says "Export Tree". Click it and then save the file somewhere you'll be able to find it (I always recommend Desktop if you're not computer savvy).
When you load up WikiTree.com, click on Add on the top right hand side and then scroll down to GEDCOMs. I highly recommend reading all the information because, once uploaded, you're going to have to wait for an email to let you know when it's been processed and then you'll have to compare your tree against pre-existing pages. It's easy to do if you take the time to read the directions, but it's overwhelming if you just try to jump in. Save your progress often just in case.
