Jade4

My suggestion on solar panel replacement would be 4 x Ja 550w or if you have space 5 x JA 550w 5S1P the latter will work great providing ~210v Vmp @ 13A. Below data sheet of the JA panel range you can consider. I have use these panels in my installations and they work great with the 5kw Sunsynk.
JA-Solar-525W-550W.pdf

You would have to look for panels that fit the situation, as in panels that would be *more* than 40V Vmp each and not exceed, ideally 13A Imp, if you want to fit 4 new panels, replacing the existing 4, but also size wise, as in dimensions, you'd have to try and find something that works for your installation... otherwise, yes, series up the 4 new panels and connect them in place of the existing ones...

I can highly recommend @Leshen 

Try this: On the inverter's screen, find the Status Page, and then give the values for Volts in the blocks for Solar Power 1 & 2.
My guess is it's around 125Volts, give or take a bit, when the sun is shining.

The MPPTs on the 5kW Sunsynk can handle max 13A. Anything above that gets clipped. Based on your panels VMP, you will max produce 408W per panel (31.4V x 13A).
So any panel with an IMP around 13A will do.
In theory you can mix panels, but it is a whole mess. I would advise against it.