What does it consist of ? Is there a separate amp ? What power ?

I want to upgrade the system but understand firstly what's there. I have a 2003 325ci with the standard 6 speaker sound. It appears to have 6" paper cone 1 way speakers on the rear parcel shelf and 5" speakers in the front doors plus tweeters in the front doors.

Any information appreciated, also anyone know what type of screws hold in the rear speaks ? They have a pattern on them (not slotted, not posi and not torx)....

any info appreciated, thanks,

Seedar.