The Update dropped the ROBLOX browser completely allowing you to play directly from your Internet Browser. So you do not need to install Roblox, all you need to do is go to Roblox.com and log in then click play on the game you want to play. Be sure you have pop-ups enabled from Roblox and it should just launch from there.
If you continue to have problems, please write to Customer Service at info @roblox.com.