Fig 1. Smooth Menu

<6> - Painting

Press and hold the <6> key to smooth the mesh at the mouse pointer location. You can adjust the degree of smoothing under the Brushes panel.

<E> - Smooth Everything

This will smooth the entire mesh, even the hidden parts. You are asked for the smoothing amount, and then <Y> to confirm before the anything is done.

<G> - Smooth Marked Area

Or you can use the <G> key to mark an area out first, then use <6><G> to smooth just that area.

First you will be asked for a Border value; this is the area outside of the marked faces that is used to blend in the smoothing. Next you'll be prompted for the smooth amount itself, and then finally the affected area will be shaded blue and you are asked to confirm with a <Y> key if the modification should proceed.

Fig 2. Options

Additional Options

If you click on the gray Smooth button in the Brushes panel, then some additional options are shown (see Fig 2). Click on the Smooth button again to hide these away.

Normal 

...

Volume 

Volume preserving

Color 

only color