HI all, bought a used Sundance Calypso spa - 1996 manufacture.
This spa is fitted with a circulation pump, and then a 2 speed jet pump.
In the manual it says I should be able to press the jet button once for low speed and a second time for hi speed. But doing this only turns the pump on or off.

I think it's low speed - not sure. When the whirlpool jet is on, the whirlpool seems very strong. But divert it to the other 17 jets and it's very weak. Also, the air valve going to that jet doesn't seem to make any difference if it's open or closed. The jets look like 100% water with no extra air.

I have a 50 amp 240 volt power supply to it so the spa has plenty of juice.

The book also mentions that it's possible to have the dealer modify the circuit board so the spa only draws 30 amps instead of 40 but the heater won't work at the same time as the pump. I don't know if this has been done to my spa.

How do I test the pump without blowing anything up? Anyone have experience in these? Have attached some pics for reference.

the manuals you are reading are likely USA manuals - SD spas are different for the export models having single speed main pumps in almost all instances.
i suggest you contact me directly for local support, correct manual, and parts
you do not have a 50A requirement - only needs 16, 20, 25 or 32A depending on jumper settings selected with load shedding
we have much lower current draw on pumps here in Australia and also use smaller heaters.