Windows 10 Is Now Live.

Hundreds of thousands of users will update today. Some will work fine, others will not. My advice: Avoid ranked games AT THE VERY LEAST for today as the impact is unknown to the League Client / the individual computers - etc. You are at higher risk for latency / afk's / visual issues that negatively impact performance as a result of drivers needing updating that aren't necessarily available yet.

Personally I wouldn't do ranked until at least a week has elapsed to give the hardware folks time to write and test new drivers. Just my opinion and to each their own! Happy hunting!