First of all you go to: \steamapps\common\Rakion\Scripts

Then open OptionData with notepad(++)

and copy this

<ScreenOption IsFullSceen="true" ResolutionWidth="1920" ResolutionHeight="1080" />

to the first line of text after
<OptionList>
<SystemOption>

Have Fun with the Nostalgia

It may have bugs in loading and waiting screen because its not intended but its works perfect in game