3-1/30 is pretty old. It's just about the last of the 'full screen' software, I assume you have a 4:3 monitor and not the wide screen version.
There are 2 things you need to be aware of upgrading a Mk III from this type of software :
1) You will need a key CD.
2) The Nav software CD must be a Mode 2 Form 1 disk, if it's not then there is a high probability that you will brick the MK III.
There are plenty of images of the Nav CD software disk about that contain the last version of the Mk III software, 3-1/63 (V22 on), but many of these are not the correct format for the Mk III, they work fine in the MK IV.
This is a link to a version with the correct format, but you still have to burn it correctly.
Bottom line, unless you know what you are doing, or willing to accept the reasonably high risk of upgrading a MK III, don't do it yourself.