DataBase poorly designed

I don´t know if I can made this kind of question here so previously I apologize.

I work with a system that has a lot of dependencies and a DataBase poorly designed. Now I have to make a decision and would like to hear some cases of you people.

That´s the case: Some part of the software was made without thinking in all cases of uses. Today I need to do severe changes like creating new relations on the database, refactoring all the classes and methods. That´s what the theory says, but in pratice this will take a lot of days, will delay the version and the entire schedule. I have the option to keep the gambiarra(bad code that works) and make just the little changes that meets the new needs.

I know that each case is different, so I want to hear what would you do and if have you been through something similar.