I'm working in AgExpert 2016-03. Somehow, whenever I do a Capital Asset purchase to Class 8, it is defaulting to Class 10.1 and I don't know how to change it
That just means that the account number you are choosing isn't linked in your CCA/Depreciation setup. Click on your Setup menu and choose CCA/Depreciation and make sure that the account you are trying to use is linked to your Class 8 assets there. Once that link is established then it will show properly as class 8 instead of class 10.1.