This sounds like you're relatively new to the company - if so you might want to take a little time to really get to know the codebase and understand the busines

This sounds like you're relatively new to the company - if so you might want to take a little time to really get to know the codebase and understand the business better. I can certainly believe that there is no will to try to upgrade the code if it's horrible and poorly documented. The question I have is, would they be more willing to update it if they felt safer doing so? If you think they would then you could offer to put some tests in place to help you get a better understanding of the codebase. Once there's some tests in place that people can use to make sure their changes haven't broken anything then they might feel more comfortable to make changes.