Upgrading Pip on Windwows using Pip itself - PermissionError

I am trying update Pip on Windows using command:

pip install --upgrade pip

However I've got this error:
'File "C:\Python34\lib\site-packages\pip\utils\__init__.py", line 73, in rmtree_errorhandler
raise
PermissionError: [WinError 5] Access is denied: 'C:\\Users\\Petr\\AppData\\Local\\Temp\\pip-8u1yrmna-uninstall\\python34\\scripts\\pip.exe'

Solution?