Here is a decent guide for Overclocking FM2 Chips take a look, it is not on a ASUS but the basics are covered and it will give you a decent feel for the process.
http://www.ocinside.de/workshop_en/amd_fm2_overclock/
Here are some basic explanations of what your Asus Bios has, compare them to the Above before you start.
http://www.tech-critter.com/2015/03/unboxing-review-asus-a88x-gamer-gaming.html
http://www.anandtech.com/show/7948/asus-a88x-pro-review/4
Here is a more detailed Video of the Asus Board you have but it is not in English, once you are familar with the Above 3 then look at this one.
https://www.youtube.com/watch?v=8r71oFfWfmk
By now if you have consumed all the above then you should be familiar enough to give it a try, I would give EZ Mode a shot first and see how high it will go my guess would be 4.3ghz. The process wont change regardless which CPU you have and all FM2 CPU's will also perform better with faster RAM, when I build a FM2 system I use 1866mhz or better and overclock the RAM timings to whatever max I can find stable. I hope you find this helpful for me just to tell you what to change wont help you learn what is going on, these however will give you a good feel for the Task.