ERPNext app installation error

Hello

I have followed the steps mentioned in the github repo GitHub - frappe/bench: CLI to manage Multi-tenant deployments for Frappe apps and at the point of command execution bench get-app erpnext https://github.com/frappe/erpnext i am getting below error

INFO:bench.app:getting app erpnext
fatal: destination path 'erpnext' already exists and is not an empty directory.
Traceback (most recent call last):
  File "/usr/local/bin/bench", line 11, in <module>
    load_entry_point('bench', 'console_scripts', 'bench')()
  File "/home/frappe/ERPNext/bench-repo/bench/cli.py", line 40, in cli
    bench_command()
  File "/usr/local/lib/python2.7/dist-packages/click/core.py", line 716, in __call__
    return self.main(*args, **kwargs)
  File "/usr/local/lib/python2.7/dist-packages/click/core.py", line 696, in main
    rv = self.invoke(ctx)
  File "/usr/local/lib/python2.7/dist-packages/click/core.py", line 1060, in invoke
    return _process_result(sub_ctx.command.invoke(sub_ctx))
  File "/usr/local/lib/python2.7/dist-packages/click/core.py", line 889, in invoke
    return ctx.invoke(self.callback, **ctx.params)
  File "/usr/local/lib/python2.7/dist-packages/click/core.py", line 534, in invoke
    return callback(*args, **kwargs)
  File "/home/frappe/ERPNext/bench-repo/bench/commands/make.py", line 30, in get_app
    get_app(git_url, branch=branch)
  File "/home/frappe/ERPNext/bench-repo/bench/app.py", line 62, in get_app
    cwd=os.path.join(bench_path, 'apps'))
  File "/home/frappe/ERPNext/bench-repo/bench/utils.py", line 127, in exec_cmd
    raise CommandFailedError(cmd)
bench.utils.CommandFailedError: git clone https://github.com/frappe/erpnext  --depth 1 --origin upstream

Any help to solve this would be appreciated.

you already have erpnext folder in your /apps directory, remove it first