The Preferences window can be opened by going to Extensions > Thea Render > Preferences.

General Tab

In the General tab you can change the plugin's language. Select one of the supported languages from the drop-down and restart SketchUp for the changes to take effect.
Autosave every (minutes): When Auto Save is enabled, Thea automatically saves the rendered image every 10 minutes (this is the default time, but you can change it). To find the Auto Save location, go to the Console of the Rendering Window.

Interactive Render Tab

Initial Appearance: Use the slider to find the best balance between rendering quality and responsiveness. The more responsive, the less precise the initial frame.
Resolution Reduction for IR Overlay: You can render at the same resolution as your monitor, but this is not practical when you have a high resolution monitor. The resolution reduction option lets you reduce the rendering resolution so you can render faster (the image still maps correctly to SketchUp view). It is highly recommended to use resolution reduction if you have a 4K+ monitor.

Channels Tab

Use the Channels preference panel to select a format. For EXR, you can select a bit depth for each channel. Note: Not all channels require 32-bit depth; only some (e.g., position, depth, and UV pass) will benefit from 32-bit depth. To save the render passes as one multi-layered EXR file, enable the option “Create multi-layered EXR including all channels”; otherwise, each channel will be saved as a separate file.

Advanced Tab

Warm-Up: If Warm-Up is turned on then an initialization phase will take place in order to accelerate render convergence. It will take longer before ray tracing phase actually starts but image noise will clear faster in the presence of multiple lights in the scene (with overall lighting being also more accurate in some cases).
Reduce SketchUp color values: When enabled, Thea prevents the use of RGB values higher than 220 to reduce the impact on render times. This also affects the brightness of SketchUp textures.
Show all material properties: By default, the full Thea Material Editor hides advanced settings to keep the user interface cleaner. While these settings can be accessed from the advanced settings icon, you also have the option to have all the properties visible at once.