ST4 cannot load ST2.5 sounds, You will need to Import them into ST3 and then access the ST3 library from ST4. Yes, it's a bit of a pain.
If you have Registered ST2.5 then the Sounds Library downloads should be in your User Area. At least, mine are -but I would have to buy a Downloads Reactivation Credit to get them again. As yours do not show then contact Support who can look at your User Account and see what's going on.
Nobody here has any access to your User Account.
But you will also need ST3 installed.
Please see
https://cgi.ikmultimedia.com/ikforum/viewtopic.php?f=12&t=24083