Eliminate complex if else through proper software engineering principles

A CRM System exists where lets say there are 60 different order types for 40 different products. Processing of each order for each product is different though there may be similarities. Code for the process logic of these orders involves complex if else statements. Change in a code is extremely risky as it often breaks consistency somewhere else because of long and complex if else. It is very hard for the developer to keep track of if else.

How can the system be designed with OOP principles or otherwise, so that we can limit the the effect of code change only to that order type and product.