I should also add that I got errors on half of the rows when I tried to upload them with the error message "Record has been changed" so clearly there is an issue in either the format/content of the file or how I am uploading using the import wizard. Any advice would be really helpful.

Hi thanks for getting back to me so quickly. So that was the process I used and I have 11 files to upload because of the amount of data I need to update. This is what the upload file looks like. It took an hour to update the first 25,000 row file. Any idea what I am doing wrong or if there is a way to make it quicker?…