Use a prying tool, such as a spudger, to separate the foam filter from the larger HEPA filter.

As mentioned previously, a lot of fine dust can kick up during this step, especially if your vacuum is extremely dirty. Consider using a mask if necessary.

The picture shows a pencil being used, which works fine, but take care to not puncture or otherwise damage the foam filter.

Set both of these aside with the rest of the filter assembly for cleaning later.