1. Download and install Tortoise SVN from this link:
TortoiseSVN2. Go into your garrysmod directory(where your hl2.exe is located) and right click on empty space. Choose SVN checkout from context menu and you will see window like that:
3. Type
http://facepunch.svn.beanstalkapp.com/gmodgame/trunk/ in URL of repository field and replace gmodgame in checkout directory to garrysmod_english. After that you should have something like that:
4. Then press OK and wait before checkout will complete(there ~1.3Gb of files).
5. Ok, now run your Steam and go to Library.
6. After that press right mouse button on Garry's mod, and select Properties.
7. You will see this window:
8. Go to Set launch options and this window will open:
9. After that type -game garrysmod_english in field to get next result.
10. Now you can launch Garry's mod and new version would launch
P.S You'll be able to update this gmod version in similar situations without waiting Valve.
P.P.S Alternative: wait for Valve.