Redesigning software application: Looking for a framework!

At the moment I'm redesigning a software application. But we noticed that not everything is necessary to be redesigned, like CRUD screens, etcetera.

We are looking for a 'framework' to plot the different features on to create clarity in the process of:

• what we need to redesign
• what we can keep
• what we have to research on, etcetera.

Is there a framework for these kinds of things? Maybe I'm overthinking this, but I want to help the business to have a more precise roadmap for the quarter's planning. Also, to keep in mind which things we have to do more research on, revise the information architecture or design. Otherwise, we are just making the same software but only with some new fancy colors/typography, and that's not what I've assigned to do!