There are several filters grouped together in the Blur category in the Filters menu. All of these filters blur images by searching out areas of strong color contrasts and sharp edges, which are then softened by converting pixels in the relevant areas to an average of their total color values.
The most basic and quickest filters to use are:
Blur
Blur More
Heavy Blur
None of these brings up a dialog for you to make your own settings and there is no way to preview the results. Essentially they are a rough and ready way of averaging the sharp contrasts in an image, though without being susceptible to fine control. As the names suggest they are, in ascending order, relatively stronger than one another in their effects.
The following Blur filters give you much more control:
See also: