Are you using Unity or Flash to play?
Try upgrading your RAM to at least 8GB, ideally 16GB. It might be worth upgrading your GPU as well. I have 8GB RAM and 2.20 GHz. You could run a full anti-virus scan; if there are any viruses, remove them. You could also clean your disk (https://danchurchblog.wordpress.com/2017/04/26/deleting-temporary-files/
) and defragment your drives (https://danchurchblog.wordpress.com/2017/04/26/defragmentation/
Sometimes, restarting your browser once in a while helps - clears your browser's RAM; browsers can be memory hogs.