Ruby on Rails -- How can I update ruby to >= 1.8.7

I've been trying to figure this out but its starting to make me want to pull my hair out.

I'm installing RoR on a new machince using instantrails.

Whenever I run "gem update --system", I get the error for several gems? that "activesupport requires Ruby 开发者_StackOverflowversion >= 1.8.7"

I run "ruby -v" and it returns "ruby 1.8.6 (2007-09-24 patchlevel 111) [i386-mswin32]

I am using Windows Vista.

I've already been to http://www.ruby-lang.org/en/downloads/ and install the latest version of ruby into the C:/ directory....but still the version remains the same.

How can i fix this?

Install using Ruby Installer.

Ruby 1.8.7: Download link.