Windows 7 still does what I need it for, for the most part, but since Lumosity upgraded their site, the games are laggy for me now. I contacted them about it with my system specs and was is the reply:
There are several factors that could contribute to how fast our games load on your computer, such as: the age of your computer, the browser you’re using, how much memory your computer currently has, and other programs running at the same time as Lumosity. Certain browsers, computers, and graphics cards run HTML5 more smoothly and quickly than others.
If the steps we've suggested haven't helped, then you may want to consult a technician for assistance in speeding up your computer in general.