Updates from 1.6 to 2.1 are a lot.
It would be wiser and safer to re-download and upload the new files
To be extra safe,
Please backup your Database before you start,
Then download from ThemeForest
and upload to a folder called circleflip2 or something like it
don’t replace old files, rather have 2 theme with 2 versions
After uploading, activate the new version and check your website
feel free to delete the older version if you would prefer after you make sure that everything went okay with the new one.