You don't really need to do anything to claim the extra storage space. When you open up the Settings section of the Play Music site, Uploaded Songs should now reflect that you can store a maximum of 50,000 songs.

So how does Google Play Music stack up with the competition for storing your music library in the cloud? Well, Apple's iTunes Match service will store 25,000 songs, half of what Google now offers, and iTunes Match will run you $24.99 a year. Amazon, meanwhile, will let you upload just 250 songs for free, though a $24.99 annual subscription puts that limit at 250,000.

As a reminder, music purchased on the Google Play Store does not count against your storage limit.

Source: Google