(This is tested on my pc but may vary based on your pc/ tested on windows I do not know how it works for a Mac)

As you probably have or haven't figured out yet you can't change the resolution of the game in its in-game settings. To do this you will have to change it in the actual properties of the game itself. First you will need to open windows startup menu, next go to My Documents, then find My games and open the file, You should come across a file named HZ open this, Next go to SeaGame File and Open that, Next go to the file that is named Config and Open it, Finally open a file named SeaGame Options, You should come across a notepad file with a config like this:

(Warning Please make a copy of these settings in case you mess it up, I will not take responsibilty if you mess up your own game)

[SeaGame.VideoSetting]
ResX= 1024
ResY= 768
Fullscreen=True
VSync=False
Bloom=True
LightShafts=True
SniperMode=True
WaterReflection=False
CharacterDetail=True
WaterEffectEnable=True
WeatherEffectEnable=True
AircraftShadowEnable=True
Brightness=5
EnvironmentQuality=1
CharacterQuality=0
TextureQuality=0
ParticleQuality=0
AntiAliasingQuality=0
ShadowQuality=2
DisplayQuality=0

[SeaGame.SoundSetting]
MasterVolume=80
BGMVolume=80
AmbientVolume=80
FightVolume=80
VoiceVolume=80
SystemVolume=80
SpeakerVolume=80
MicVolume=80
AutoJoinChannelEnable=True

[SeaGame.GameOptions]
CheckMultiGPUMode=True
ConfigVersion=2

To change the resolution you will need to change the input of ResX & ResY which are set at default of 1024 & 768 or 1024 X 768 Resolution Size, you can change this to the desired Resolution Size then save the file not save as but overwrite the file. Close all the files you opened, start up the game, then go to settings in game > Graphics, and it should say the new designated Resolution Input you set. If it isn't at the designated Resolution you set you may have done something wrong. (May not always work)