how to move 9.1 ports to HEAD?

[Anton Shterenlikht]

I just installed 9.1-release including the ports tree:

root at zzz:/usr/ports # svn info /usr/ports/
Path: .
Working Copy Root Path: /usr/ports
URL: svn://svn.freebsd.org/ports/branches/RELENG_9_1_0
Repository Root: svn://svn.freebsd.org/ports
Repository UUID: 35697150-7ecd-e111-bb59-0022644237b5
Revision: 311939
Node Kind: directory
Schedule: normal
Last Changed Author: beat
Last Changed Rev: 307934
Last Changed Date: 2012-11-28 20:30:08 +0000 (Wed, 28 Nov 2012)

root at zzz:/usr/ports #

I want to move the ports tree to HEAD.
Is there an easy way (i.e. not involving
rm -rf /usr/ports/* and then a fresh svn co)
of achieving this?

I tried "svn switch" and "svn relocate",
but it seems these are intended for just
changing the root URL, i.e. when the tree
itself is not changing.

Please advise

Thanks

Anton