myTaxExpress and T2Express software update on Mac is different, because of the difference of computer system between Windows and Mac.
On Mac, you only need to re-download the latest Mac version software from our website, and remove the old software. Your data file is under "\\my documents\mytaxexpress", which is not under myTaxExpress or T2Express software folder. So you won't lose data file.
After downloading the myTaxExpress Mac version .zip file, you can right click the mouse and choose "Open", it will unzip the software into a folder called "myTaxExpress<year>_mac".
You can find the myTaxExpress software under this folder.