How to upgrade to Solr4.0 to use Result Grouping?

[Ruixiang Zhang]

I want to use the Result Grouping feature that's only available for Solr4.0.
Currently, I have Solr1.4.1 installed.
I want to know how to upgrade it to Solr4.0 so that I can use Result
Grouping?

Thanks a lot!!!
Richard