Uninstall ruby 2.1.3 installed from source


I have a similar question to the above thread and I am new to ubuntu and

I have installed ruby 2.1.3 from source and ruby 1.9.3 from package
(sudo apt-get install ruby1.9.3).

Now I want to keep 1.9.3 and get rid of 2.1.3 version.

gem list
*** LOCAL GEMS ***
bigdecimal (1.2.4)
io-console (0.4.2)
json (1.8.1)
minitest (4.7.5)
psych (2.0.5)
rake (10.1.0)
rdoc (4.1.0)
test-unit (

I tried to gem uninstall bigdecimal.
ERROR: While executing gem … (Gem::InstallError)
gem “bigdecimal” cannot be uninstalled because it is a default gem

ruby -v
ruby 2.1.3p242 (2014-09-19 revision 47630) [x86_64-linux]

pkg-config --list-all | grep ruby
ruby-2.1 Ruby - Object Oriented Script Language
ruby-1.9 Ruby - Object Oriented Script Language

Should I remove ruby1.9.3 through package manager first and then trying
to manually delete /usr/local/bin/ruby. And then afterwards reinstall
1.9.3 through package manager?