ROBB not changing a thing will work. But not as good as it can be.
I have a Two element cubicle quad built on the test tower. spacing is 108" between the driven element and the reflector. 10 gauge stranded teflon coated wires for the elements, Design freq is 27.300 mhz. Gamma match for impedance matching,
The 2:1 VSWR bandwidth according to the mfj259B analyzer is 26.000 to 29.999 mhz. Almost 4 mhz. Quads do have a low Q,
Reactance of X=0 is almost the whole 40 channels of 11 meters.
The bottom of the elements are 4' off the ground.
I was checking the F/B turning it East to West looking at how much rejection it had. About 15DB as to be expected on a long boom two element.
So I decided to key into it and see what happened.
I made a contact on 38LSB last weekend to a mobile in San Diego.
It was not the antenna, it was propagation.
If the original poster wants a 4 element yagi for 10 meters then it needs to be designed for the center frequency of the portion of that band he wants to work. CW/ Phone/ AM/FM ???
Many online calculators for yagi design. Google is your friend.
I do not own a sirio antenna. Probably never will, I build my own.
If you are looking to purchase an yagi and be able to adjust it for 10 meters look at Macos. or Look at Mosley, cushcraft etc. Also QTH.COM usually has some mono banders on the classifieds boards for decent prices.
I use a stock 4 element Sirio beam on 10m with great success; didn't change a thing. All I did is use an antenna tuner and that was enough. Used it up to 28.5mhz USB this way. Talked to Moscow three times and got a 10 over 9 report with less than 100w as well; Mongolia and Malaysia too. Smoked many who use a tribander, simply because it is a monoband beam - IMO. Of course, conditions were favorable.
You could re-tune it to the 10m band; but I have no idea why you would go to the trouble unless you don't have a tuner.
Changing it to a 4 element is a matter of just adding some homebrew parts to it and measuring the lengths.