How to switch git user at terminal?

I am trying to push a project to a remote repository from the command line.

From inside my local directory, I hit:

$ git push

and obtain the following error:

remote: Permission to useame1/repo.git denied to useame2.
fatal: unable to access 'https://github.com/useame1/repo.git/':
The requested URL retued error: 403

Where useame1 is my github account useame hosting the repository I want to push to and useame2 is an old account I used to use on this machine.

I am using OS X Yosemite (v10.10.5) on a Macbook Air.

How do I correct the user issue and successfully push to my remote from the terminal command line?