Resolution: The dimensions of your image in pixels. "Lock aspect ratio" can be used to easily re-size an image (i.e. same proportions, different resolution) and is on by default; if you would like to change the image proportions simply uncheck this before entering the new resolution.
AA level: A higher AA (anti-aliasing) level results in finer details and better anti-aliasing, but requires more memory. Changing the AA level will restart the render. Generally, AA level 2 makes great images, but you can use 3 and higher for exceptionally detailed images, or ones with sharp bright edges. When rendering for prints, AA level is not as important as reaching high DPI via image resolution, and AA level 1 is often used in this case.
Save alpha channel: Used if you want your IFS to have a transparent background. Does not restart your render.
- Anti-aliasing mode: A selection of different filters used when anti-aliasing. Changing these does not restart the render. If the AA factor is set to 1, the different modes will have no effect.
At any time, you can press F5 to force-update the render preview, or Pause to pause the render. Pause also resumes a previously paused render.