I have the same gen - the fuel filter can NOT be pre-filled since it sits on its side.
the filter is held in by a bracket (2 bolts) that bolt to the side of the cabinet (accessible from the outside, just below & to the right of the access door)....it is NOT necessary to remove the two bracket bolts to remove the filter.
FIRST - use two wrenches to loosen each of the fuel lines on the filter FIRST.
NEXT - remove the single nut on the fuel filter/stud that holds the filter to the bracket
REMOVE / Replace filter - then replace the fuel lines (use the backing / 2nd wrench, as you did to remove the fuel lines)
once you have the filter replaced and the fuel lines back on the filter - PRIME the filter by holding the start/stop button in the STOP/Prime position until the pump/prime stops....prime the filter a couple of times & THEN start the generator & check for leaks.
oil and filter changes are called for every 250 hours
fuel & air filter change intervals are called for every 500 hours
the following document / link should be helpful (see page 3-6 / figure 3-4 for fuel filter location).
http://www.norwall.com/product_pdfs/1392_10_0hdkca_11506_om.pdf