Make sure you are in "enable" mode, then use the "show flash" command to list the files in the NVRAM. Here is a section from the AOS Version R13.12.0 Command Reference Guide 60000CRG0-35AV PDF.
>enable
#show flash
Files:
245669 010100boot.biz
1141553 new.biz
821 startup-config
1638 startup-config.old
1175679 020016.biz
821 startup-config.bak
2572304 bytes used 4129776 available 6702080 total
System image file is “020100.biz”