Hi, Steve,
The photo is a bit small for my old eyes and pixelates if I try to enlarge it but,
I am almost certain there is a knob on the left side of the blade.
With the lever on top of the arm in the UP position
If you turn that knob (on the left of your blade) counter-clockwise, it will loosed and you can remove the
blade from the top blade holder or blade clamp. There will be another knob
on the bottom of the blade which works the same way.
Once you remove the blade, you insert a new plain end blade in the bottom clamp
and tighten the knob.
Now you can insert the blade through any fretwork you are cutting and put the blade
in the top clamp, turn the knob clockwise to tighten it and that is what holds the blade in
the clamps.
Theoretically, if you tension the blade by turning the lever clockwise and then lock the lever down,
you can then release the lever, remove the blade from the top clamp at the same heigth that you had
it in originally and lock the lever down again and the tension should be set. That is in THEORY ONLY.
I would release the lever and turn the lever counter-clockwise when you want to go from one entry hole
to another, insert the blade then lock the lever down and gradually turn the lever clockwise until the tension
is tight. It is not necessary to put a lot of force or tension on that lever. Once it is tight, it is ready to cut.
Please let us know what you learn as you go.
I looked for the model number you listed and kept coming up with a mitre saw instead of a scroll saw.
God Bless! Spirithorse