On a Win10 PC, go to Settings > System > Display > (all the way down) Graphics settings, then click Browse and select the Eternum.exe, and finally select "High performance". This window will also tell you if you have a base and a high card, if you have no choice then that's it.
Sorry if this does not solve the issue - hopefully v0.6 will help you or write to Caribdis with the version you are using and a brief summary of you settup (OS and OS version, graphic card and current driver version, which .exe you are using (Eternum vs Eternum-32)) and they might be of better help