Hi! Try downloading the older client and see if it helps! The new update should not make the game slower for you.

Here is the link to the older client: http://img.oasgames.com/upload/1468827100/NarutoOnline_en_2.3.0.7181_oas.exe

~Jib

If you are using the older version already, I recommend trying the newer version and seeing if it helps. If it does not, you might need to submit a ticket to customer support so that they can further assist you. You are lagging even with a complete system reboot right? Or does it lag over time? If it lags over time, you need to go to task manager (ctrl+shift+esc) and end task all the NarutoOnlineen.exe instances. You could also create a shortcut that kills all tasks of a specific application.

Here is where you can find the new client: Click Here

~Jib