Correctly upgrading ruby on MS Windows

Hi, I am looking for some guidance on the correct and/or most
streamlined way to upgrade Ruby. Presently I am on Ruby version 1.8.6
patch level 111. I am looking to upgrade to version 1.8.6 patch level
287. When I tried downloading the ruby-1.8.6-p287-i386-mswin32.zip
file I unzipped it and was optmistically hoping that i could take all
of its files and overlay my current installation. When I checked the
rails version with (rails -v), I get the following error:
D:\Mercury\GreenLight\server>rails -v
c:/ruby/lib/ruby/site_ruby/1.8/rubygems.rb:713:in `set_paths':
undefined method `uid' for nil:NilClass (NoMethodError)
        from c:/ruby/lib/ruby/site_ruby/1.8/rubygems.rb:711:in `each'
        from c:/ruby/lib/ruby/site_ruby/1.8/rubygems.rb:711:in
`set_paths'
        from c:/ruby/lib/ruby/site_ruby/1.8/rubygems.rb:518:in `path'
        from c:/ruby/lib/ruby/site_ruby/1.8/rubygems/source_index.rb:
66:in `installed_spec_directories'
        from c:/ruby/lib/ruby/site_ruby/1.8/rubygems/source_index.rb:
56:in `from_installed_gems'
        from c:/ruby/lib/ruby/site_ruby/1.8/rubygems.rb:726:in
`source_index'
        from c:/ruby/lib/ruby/site_ruby/1.8/rubygems.rb:138:in
`activate'
        from c:/ruby/lib/ruby/site_ruby/1.8/rubygems.rb:49:in `gem'
        from c:/ruby/bin/rails:18

I also saw that ruby/script console and ruby script/server -e commands
also failed. I've tried renaming the current c:\ruby directory and
just creating ane c:\ruby directory with just the patch level 287's
contents and that fails because some of the binaries are missing.
Which gems and/or plugin require reinstallation after a correct
upgrade? Please advise?