How i fix the lag than makes my game slower when i play on multiplayer? i mean, i don't lag at games but always when the game start to advance or big fights start to become my game just turn slowly and i just can't micro my units how i want to

This happens when your system is not able to cater to the requirements of the game thereby resulting in a drop in frame rate to compensate load on your GPU. Long story short your computer cannot handle 8 player games with large world populations.

Here are a few suggestions:

1. Upgrade your computer and/or its hardware.
2. Run a hardware test to make sure you don't have faulty disks or ram sticks.
3. Make sure you close every single application before logging into Voobly. Ensure there are no open browsers, cloud sync agents, scans from security apps running in the background. In short nothing other than Voobly and AOC.
4. Double check if the system is getting overheated. Overheating is a very common cause of increased CPU and GPU usage which simply adds to the existing problems. There are tons of temperature monitoring apps and if you find this to be the cause, you know what to do.
5. If you happen to use your machine in an open or dusty environment and you haven't cleaned your system (internally) you will be surprised how much of a difference this can make.

Other workarounds can include optimising your GPU to lower down the display quality. Resolution also plays a very important role. If you can afford to play at a lower resolution, you will notice significant improvements.