A "revision" is a change that you make to a document that has already been finished or published. To "make revisions to ___" means to change part of something.

You can also use the verb "revise" instead of "make revisions". In the example at top, that would make the sentence:

Albert is asking us to notify him whenever we revise the extensions sheet.

There's not a really strong difference between this version and the original version. But I think the original version sounds just a little more natural.