Sounds like there's no source control... So you should just pick things off bit by bit. Don't rewrite, especially when you have no process to roll-back. - Sour

Sounds like there's no source control... So you should just pick things off bit by bit. Don't rewrite, especially when you have no process to roll-back. - Source Control - CI/CD process - Lock down production so there's no access - Kill off dead code - Start organizing and refactoring etc... Edit: Alot of people have already said the above. But I want to add. Just because code sucks and is messy, obscure, has no structure or breaks everything we learn as developers that define 'good code' or 'good coding practices'... does not really mean it's bad if its generating the business money. It can often be quite fun to work on because everything is a win, performance, cost reduction, easier maintence, etc.