Fitting a new electric shower...

Re the electric shower, currently there is a Mira Jump 8.5kw unit there (not the multifit model) and I’m wondering if a 10.8kw or 9.5kw model can replace it using the existing supply, but I’m confused because the breaker is 32amp and even for the current 8.5 shower Mira talk about 40amp ( same for the 9.5kw ) and 45 amp for the 10.8kw. It says 2 x 6mm + 2.5 and the isolation switch doesn’t say anything externally?