If you had a Mk-IV and software v27.1 you should already have the perspective view option. Are you sure your unit is reading maps from DVD?

Anyway, even if you have a Mk-III you can upgrade to V29.1, but only after making absolutely sure your V29.1 software disk has a "mode 2/form1" data format. If that is not the case your unit will block itself.
And then, you will see no difference, if you actually have a Mk-III.

Regards