....Here is the fare if anyone cares to look it up: QLW50BSP. The way I read the fare is that you are permitted one inbound change with no reissue fee....
Have you flown your outbound?
If not, entire ticket needs to be re-priced with fee and fare difference. Once you have flown your outbound, the inbound can be changed with according to fare rules. Of course, the availability can change and your desired date may no longer be available.