How to delete information on Storage

Hi, I need some help with two servers, they are running on AIX 5.3, we want to remove and delete all information stored on them because we are no longer to use anymore. The servers are going to be part of donation and we want to be sure that no one can restore information stored on disks or storage.

How can we do that?, exists command or free tools to do that?

Thanks in advance.

just boot from an external media and use "dd" to write zeros to your disks...