Cases should be defined by the size of motherboard they can accomodate.
That case looks like it could hold a ATX motherboard which will have 7 expansion slots.
It could be a Micro-ATX which has 4 slots.
A ITX will have only one.
A full tower will usually have room for a large number of hard drives, like 6-8+ and 3 dvd drives.
A mid tower will have 1/2dvd drives and 4 -6 hard drive slots.
To know what you can change, find out the exact model of the motherboard. CPU-Z will identify it.