please open a support ticket and reference this tread. We will help you to get this done.
I support ticket is open but I'm not getting any progress with it so I thought I'd try posting the question.
If you are running IPAM v1.5 you can change this for going forward by leveraging this utility, see IPAM v1.5 "Internal Settings" tool can help change UI defaults
As Martin mentioned, to change your existing subnets, please open a support ticket so we can assist you.