library license

[Carlos Santander]

This is a bit OT, but not exactly.
I modified Miguel Ferreira Simoes XML library to use Mango instead of Phobos 
(except for std.string.letters and similar). Now, he released it with a BSD 
style license (I think). I want to make my changes public, but I don't know if I 
can add another license (zlib) to the existing, or if I can replace it, how to 
keep copyrights, etc. Or should I just keep his license and just add my name to 
the "author" section, also update date, version, etc.?

-- 
Carlos Santander Bernal