Help me about setup RVM in Ubuntu 12.04

I 'm setting RVM for programing Ruby On Rails.
I tried some instruction and setup successfully.But ruby version is
1.8.7 and Rails 2.3.14.
I tried update Ruby by :Uninstall RVM then install curl,setup ruby 1.9.3
p125,gem install rails ....,and Ruby ,Rails version Update
successfully.. But after close Terminal the version of Ruby,Rails...
same as first (ruby 1.8.7 and rails 2.3.14...).
Someone can explain this problem for me?Thanks

rvm use ruby-1.9.3-p125@gemset --default

Hi, I installed a couple times through this tutorial:

http://blog.sudobits.com/2012/05/02/how-to-install-ruby-on-rails-in-ubuntu-12-04-lts/