changing from 20 to 25 inch

[mitch]

What is needed to change from 20 to 25 inch is there a 5 inch segment that can be added with 25 inch leg or do you have to change whole midsection.

[boats.net]

You didn't say what model you have but probably would need to replace mid section, drive shaft, shift shaft and water tube. There are some aftermarket kits available for some models, search web for extension kits.