How to refactor a Delphi unit with 10000 lines with no documentation?

Question

I have been assigned the task to refactor a Delphi unit. Wow. 10000 lines of code, no documentation, tons of copy and paste code.

THere are many methods made with copy a

Answer 1

I would use some sort of UML tool to generate som class diagrams and other diagrams to get an overview of the system, and start splitting up and commenting like @Workshop Alex said.