The AZ-ES256 is a very basic MP3 player and has no option for expanding it's memory.
If you need more memory, your only option is to buy another player. There are a number of Mp3 players around, and some have a slot to put in a microSD card to give you more memory.
You could also look at a MP4 player. While you can play movies on them, you don't need to, they will still play music. Many have 16GB of memory.
Answers & Comments
The AZ-ES256 is a very basic MP3 player and has no option for expanding it's memory.
If you need more memory, your only option is to buy another player.
There are a number of Mp3 players around, and some have a slot to put in a microSD card to give you more memory.
You could also look at a MP4 player. While you can play movies on them, you don't need to, they will still play music. Many have 16GB of memory.