10.8kw shower mira go

I would highly recommend checking installation first. If the cable feeding shower is 6mm as is common max would be 8.5 kw shower. If you add too much load to incorrect cable the cable becomes the weak link and could burn out if fuse is not rated correctly.

No! Call an electrician instead. To ask such a question you obviously are oblivious to the danger of doing this.

The cause of the tripping out should be properly understood first. ie, Is it because the shower is drawing too much current or is there too much leakage current to earth? If the RCD is tripping I really would not use the shower and would turn that circuit off at your fuse-box / Consumer unit until you get it checked out properly. Changing a device such as an RCD to a larger current carrying capacity is most unlikely to be the solution or at least all of it, for the problem you describe.