Sometimes you may need to have multiple github accounts (one for office, one for work , one for girl friend, whatever) .

Lets say you have ssh keys already setup and github is set for one account. Now for new account:

• Create a new ssh key

ssh-keygen -t rsa -C "your-email-address"

     Careful while name the file , dont overwrite the existing one .I named it as ~/.ssh/id_rsa_xxx

• Add the new key to github account

     This is simple enough. Copy the id_rsa_xxx.pub in github > Settings > SSH Keys

• Create a new config file in  vi ~.ssh/config

        Add following :

#Default GitHub

Host github.com

  HostName github.com

  User git

  IdentityFile ~/.ssh/id_rsa

Host github-COMPANY

  HostName github.com

  User git

  IdentityFile ~/.ssh/id_rsa_xxxx