below is used to add a new remote:
git remote add origin git@github.com:User/UserRepo.git
below is used to change the url of an existing remote repository:
git remote set-url origin git@github.com:User/UserRepo.git
below will push your code to the master branch of the remote repository defined with origin and -u let you point your current local branch to the remote master branch:
git push -u origin master
Documentation