Process of bringing UI changes in an Enterprise software?

I am currently working on an enterprise application which has excellent functionalities, but the look and feel of the application is pretty basic. As designers in our company we are looking into moving things look modern and usable at the same time.

So, anyone of you who have been part of any big enterprise software companies and have taken your software under go design changes how was the process there with you in bringing a change in terms of making the software look better.

Looking forward to some great feedbacks would love to know your experience on how you as a part of the team helped achieving the design goals.