You need your old password and your new password just until the files have been converted from version 1.7 to 2.
AxCrypt will not use the brute force for you. Read this page for instructions on how to use it.
You can download the current tool from here.
If you have totally forgotten the password then it will take hundreds of millions of years to recover, i.e. totally impractical. The tool is only of any use if you’ve forgotten a few characters (depending upon the length of your password) and you know the rest.