# emerge -n '>=sys-apps/portage-2.0.51'
# rm /etc/make.profile
# ln -s $(portageq portdir)/profiles/default-linux/sparc/sparc32/2004.3 /etc/make.profile
# emerge system -pv

For more information, please see:
    http://www.gentoo.org/doc/en/gentoo-upgrading.xml