Uninstall old versions of Ruby gems
# remove all old versions of the gem
gem cleanup rjb
# choose which ones you want to remove
gem uninstall rjb
# remove version 1.1.9 only
gem uninstall rjb --version 1.1.9
# remove all versions less than 1.3.4
gem uninstall rjb --version '<1.3.4'
For removing older versions of all installed gems, following 2 commands are useful:
gem cleanup --dryrun
Above command will preview what gems are going to be removed.
gem cleanup
Above command will actually remove them.