The email address you used to sign up to Kee Vault is an integral part of what keeps your account secure (technically speaking, it is part of your protection against brute force dictionary attacks against your master password).
Changing this without impacting either the security or availability of your account is an immense challenge, and one that we have yet to have sufficient resources to be able to tackle. Due to the scale of the work required we have no current plans to allow for the email address of a Kee Vault account to be changed.
If you are looking for a way to change your email address, there are currently two options:
Don’t change it at all, but consider forwarding emails from your old address to your new one (practically speaking, this is what most people do when changing email address anyway due to the difficulty of comprehensively notifying every contact of the change).
Export your Kee Vault as a KeePass (kdbx file) and then re-import it to a new Kee Vault account created using the new email address. To maximise the value you get from this, make sure you perform the task just before your old subscription is about to renew. Thus, when you have cancelled your subscription with the old email address you should be able to “win” a couple of weeks of free service via the free trial on the new account. Hopefully this will compensate for the frustration of the rather manual procedure.