Hi Chheang!
I just checked my X-Cart 5.1.4 store and it shows AudioBooks template as available in the Extensions > Marketplace section in admin area:
http://awesomescreenshot.com/0fa3a5d047
Could you please let me know what error message you are seeing? If you send me a snapshot, it will help a lot.
If you already have AudioBooks template installed, but cannot upgrade it, try to delete and install again from marketplace.
Looking forward to hearing from you.
Tony.