HDD Full on AVTech 4CH MPEG4 DVR

[Amber]

Help!
I am an IT consultant at an industrial site that was closed down for a few years, but re-opened at the end of 2009.
When they shut down, they installed 2 security cameras that recorded based on motion sensing, and emailed the clip to a security employee.
The system is an AVTech 4CH MPEG4 DVR.
I wasn't involved in the setup, and knew nothing about how this all worked.
Once we re-opened the site, security was getting way too many emails, and asked me to turn off the notifications (which I did).
I've been asked to review the security videos from last week, so logged on to the web based software for the first time in a few months.
It says the HDD is full.
All seems to be working fine, but I'm having trouble figured out how to:
1) See what available video clips there are
2) Set it so it only records movement between certain hours
3) Backup then delete all information on the HDD

If anyone can help, I would greatly appreciate it.
If I've posted in an incorrect forum, please let me know.
Cheers,
Amber