No point in confessing intelligence. My question probably gives that away. I have a two minute composition. I want to change it to 4 minutes, not just change the composition settings, but actually slow it down so it takes 4 minutes to complete and I would like to keep the best possible quality. In Premiere you choose speed, then optical, simple. I can't seem to find it in AE and since I'm asking is there a better way? I did Google, but I suppose I ask the question wrong.
Entirely depends what you actualyl need. The best way to retain quality would be to just drop the comp into a new 4 minute comp and enable time-stretch/ time-remapping (Layer --> Time --> Eanble Time Remapping... etc.) This will natively resample the time for animated properties and, within limits, also interpolate pixel-based content using the methods provided by the layer quality switches for this option. If you want a better quality, but purely optical resampling then the Timewarp (as Premiere would do) effect is your friend.
If your comp does not contain any video footage you can time remap without any problems. There will be no frame blending. The only time you need to worry about frame blending is when there is video footage or image sequences in the animation. If you do have video footage (movies) in the comp then you need to test all of the frame blending options to see which one gives you the best results.