Hi Abri Beluga,
You need to change the unit system in the VEMD Configuration Page.
This process is described in the FLM Section 7. The process is the same for all CPDS aircraft and in the EC135T3 it's section 7.12.
The process involves selecting switches in a set order, the FLM describes it best.
Any problems, let me know and I can send you the section from the FLM.