The frequency is the maximum frequency the VFD can deliver. You don't have to use the maximum frequency of the VFD.

What you need to know, is what the maximum frequency is for the lathe, so you can then set that in the new VFD.
However, if the Easiturn is anything like my old Cyclone, then they're using a VFD rated motor, that is designed to operate above the usual rated 50Hz,and IIRC the current ratings were not the same as a typical induction motor.

Ideally, you'd want to get write down all the settings from the KEB, but I know with mine, it had a PIN set, which I could never get past.