Help! Battery Install

My Golf 2000 factory battery is no good and I have purchased a new replacement. How do you remove the old battery? -- it is locked in place and I cannot see where or how to pull it from the battery compartment. Please help!

13mm bolt in the front of the battery tray behind the headlamp.

Many thanks your reply. I noticed the 13mm bolt earlier but was not sure if it was part of the battery assembly. This bolt is just forward of (and partly covered by) the battery tray cowling and behind the headlamp in a very narrow space. Is it necessary to remove the battery tray first (I tried that but the rear bolt is impossibly positioned)? Why does VW position bolts in such narrow and awkward spaces, particularly for a part that will often be replaced by a non-specialist? Thanks again your reply and any other advice would be greatly appreciated.