Hi Cheryl, the steps are:
1: On any page you should see My WikiTree on the top. Move your point over that and a Drop Down Box should appear. Click on GEDCOMs in that list.
2: Click on Browse and use the Pop Up Box to go through and select the GEDCOM file from your computer and click on the Open button to proceed.
3: Click on Upload Chosen File. This could take some time before your GEDCOMpare is ready to be viewed.
So where is it getting stuck in the above process so we can figure out what is wrong. I just uploaded a GEDCOM file to WikiTree after you posted your question and had no problems, so it is not a system wide problem..
You may also want to view this page before tackling a GEDCOM file upload to WikiTree. https://www.wikitree.com/wiki/Space:GEDCOM_File_Usage_Primer
It is a list of pages to help you with your GEDCOM file and important tips as well.