There are 2 types of "changes" - corrections and customer alterations. They are 2 very different things.
(1) When we speak in terms of "corrections", these are errors that *I* have created in your manuscript. This could include misspellings, grammar errors, etc. that I have caused. For example - I add a new chapter title and misspell it. That is a correction - it is my responsibility, and you are not charged for it.
(2) When we speak of "customer alterations", we are talking about anything YOU change after I have received the manuscript. Let's say you find an incorrect link and want to change it. This is a customer alteration, not a correction. Customer alterations are choices you make to change something that has already been done. You can be charged for customer alterations. (Fixing errors that you make are not corrections, they are customer alterations.)
Consequently, it is very, very important that your manuscript be as complete as possible before sending it to me. Don't wait to "see what it looks like" to edit it - that is liable to cost you extra money in customer alterations.
We generally allow a good measure of customer alterations without charging for them, but if it becomes excessive I reserve the right to charge for the extra work involved.