Ford used two different types of fuel line fittings on the Explorers and I am not sure of the year/engine breakdowns - but the filters will work with either type.
One is the "duck bill" type already mentioned - it uses a plastic clip with two legs and a "bill" on the top that sort of locks it into a clip. To release those, just gently pry up the plastic clip (can be white or black plastic) with a small screwdriver and remove it. The filter will then slide off the line. It may take just a bit of gentle tugging or twisting as there is an 0-ring inside the fitting that slides over the filter fittings that tends to get set in place somewhat.
The other type is a spring loaded intenal clip that requires a special tool to disenguage (as Fexplorer shared). The special tool can look a couple different ways - it is either "scissors shaped" with a sort of split metal tube at each end of the scissors (two different sizes - use the one that fits closest to the line size) and the other is usually a piece of plastic that is flat on one side and has a tube on the other (about the size of a quarter in diameter with the "tube part" the same size as the lines). This too is split so that you can fit it around the tube.
To use either of the internal tools, you open the split - press the tube part INTO the spring loaded coupler - and press. You will feel it slide past the spring and open the spring so that you can slide off the fuel filter. Leave the tool in place while you slide the filter out of the fuel line fitting. Once you do it - it will make perfect sense.
To reinsall, press the fittings back together (I like to lube the o-rings with vaseline (use a Q-tip), then either press the duck bill clip back into place or just press the spring-loaded ones together (no tool use to reassemble).
Here is a site so that you can see what the tool looks like. The site I chose even shows a diagram about using the scissors-type tool. BTW, the plastic ones usually come as a set for only a couple bucks and they will fit all the various spring loaded fittings that Ford (and others) use such as air conditioning, oil lines, etc.
http://www.mytoolstore.com/kd/kdengi04.html