Sorry, the original response was somewhat misleading...
If you are using GlassFish community distribution (i.e. jar file installer) you will not be able to use the first suggested option (installing upgrade in the same location) since jar installer does not have upgrade capabilities. Upgrade path mentioned in the reply applies only to Sun branded Sun Java System Application Server installer.
With GlassFish, you will have to install upgrade installation into different location and then transfer your domain configurations using upgrade tool (option 2 of Rebecca's reply).
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