multiple heads

[Neal Becker]

I have 3 heads.  I'm sure I just want the latest version, not sure how I 
wound up with 3 heads.
 hg heads
changeset:   636:ca6d8a69cb5e
tag:         tip
user:        ndbecker2 at gmail.com
date:        Thu Mar 19 09:53:54 2009 -0400
summary:     Add +incdir to SConstruct

changeset:   632:f927fd11da2c
user:        ndbecker2 at gmail.com
date:        Mon Mar 16 11:02:17 2009 -0400
summary:     run-tests-beta.py: init

changeset:   555:1844d569dbb3
user:        ndbecker2 at gmail.com
date:        Tue Feb 10 11:21:14 2009 -0500
summary:     merge changes from nbecker6

What's the easiest way to get rid of those other heads?