Simplify the following text for a Grade 6 native English-speaking person.
Original: The Plutonium PAK was also sold as an upgrade package to convert the first available version of Duke Nukem 3D ( v1 .3 d ) to the new Atomic Edition ( v1 .4 , later upgraded again to v1 .5 ) .
Simplified: The Plutonium PAK was also released as an upgrade package to convert the original release of Duke Nukem 3D ( v1 .3 d ) to the new Atomic Edition ( v1 .4 , later patched to v1 .5 ) .