The latest version is 7. You can look at a brochure on it's features here:
Brother® Home Sewing
I have seen upgrades from versions 5 & 6 to version 7. Not sure about upgrading from 3 to 7. Usually when the versions are that far apart, you have to pay full price for the new version.
If the program is doing everything you need it to do, I would not go through the expense of upgrading.