Use the strip command:
hg strip -r 2039
This command is provided by the StripExtension. It is distributed as part of Mercurial 2.8 and later, but you do need to enable it first by adding the following lines to your .hgrc or Mercurial.ini:
[extensions]
strip =
Before Mercurial 2.8, it was part of the MqExtension.
To prevent you from accidentally destroying history, the command will generate a backup bundle in .hg/strip-backup/ which you can hg unbundle again if desired.