Advent uses laptops from different OEM manufacturers and it sells them under the Advent brand. They don't design manuals for their laptops. To find out who is the original manufacturer of your laptop you will need to have a look at the bottom of it. Somewhere on the sticker it will have the manufacturers model number. Knowing the original brand name and model number you can easily locate your manual on 9manuals.com. Advent uses a lot of ECS chasses, so the first place to look is ECS manuals.

Advent Service / Repair / Disassembly manuals
Advent User's / Owner's / Instruction manuals