Render Options Preferences - Visualization tab

In the Menu Bar, click Edit > Preferences, then on the left side of the dialog box, select Render Options.

Render Window

Use the resolution controls at the top of this window to set your preferred render resolution. If you do not set a resolution, the render window will adapt to the size of the main VRED window.

Lighting

Progress Cursor

Adjust the progress cursor displayed during stillframe antialiasing.