While QLab v2 - v5 will update, incrementally to the next version. QLab 1 files can't!
From the QLab 2 Manual:
Transition from version 1.x
QLab 2 may be safely installed on a machine running QLab version 1.x; the two programs will not interfere with each other.
QLab 2 will not read QLab 1.x workspace files.
QLab 2 workspace files now use the file extension ".cues".
and from the horse's mouth in 2010:
"On Monday, March 15, 2010 at 12:41:46 PM UTC Chris Ashworth wrote:
Hi
QLab version 2 can't read version 1 workspace files. The program was
rewritten substantially and there was not a way to translate the
workspaces from version 1 into version 2 and guarantee they'd behave
in the same way.
You'll need to either rebuild the workspace in version 2, or, probably
the best option, is simply run the workspace as built in version 1.