Check that your Dyson DC14 is unplugged. Press the cyclone-release button and detach the bin from the rest of the machine. The cyclone-release button is the same button you push when removing the bin for the purpose of emptying it.
Set the bin aside. Note the area on the vacuum upon which the base of the bin sat. This is the cover of the HEPA post-motor filter.
Insert a flat-blade screwdriver beneath one of the three latches on the sides of the cover and carefully pry off the cover.
Remove the cover and HEPA post-motor filter inside. Dispose of the old filter.
Insert a replacement HEPA post-motor filter into the filter housing. Reinstall the cover with each of the latches aligned. Push down firmly on the cover to attach.
Place the bin back on the vacuum. Push the bin handle back toward the vacuum to lock the bin in place.