How to ISP program using USB for LM3S3748?

Hi,
I am using LM3S3748 for my design. User will have the option to upgrade the program (reprogram flash). But s/he only can do that by providing right password to make sure unknown people are not trying to upgrade firmware.

Now how can I do ISP using USB of LM3S3748? Can the MCU be reprogrammed using it's own USB ? Or I have to add serial-USB access to do that (it will be for the worst case)? Any better solution?

And how can I set a password so that without password no one can erase flash? Any code sample or any idea?

Please suggest me.

Thank you.