C:\Users\ Windows Account Name\AppData\Local\CCP\EVE\c_eve_sharedcache_tq_tranquility\settings_EveProfileName\core_public_.yaml
Open that file with a text editor, such as notepad.
Note that changing the resolution under the full screen or windowed resolution sections seems to change the resolution set in the drop down box, but not the actual resolution of the client. Once I also changed the back buffer resolution, then it finally worked.
