Here's a quick post regarding the three most common items needing replacement in a dryer vent system.
1) Transition Duct -- this is the duct that joins your dryer duct to the main duct. This should be made of heavy metal, but often it is not. There is a sticker on the back of most dryers that clearly specifies this.
2) Termination Hood -- this is where the exhaust system meets the exterior. The termination hood can be through the wall or roof (either is ok!) and there needs to be a damper integrated into it (whether a single damper or louvers). Plastic termination hoods are not recommended because most crack and break apart after a few years.
3) Main Duct -- sometimes a builder has installed an improper dryer vent and it needs to be replaced. "Slinky foil", vinyl, and semi-rigid are all insufficient materials to act as the main duct. In this case, the main duct will need to be replaced with heavy-gauge rigid material.
Each of these can vary much in replacement difficulty and complexity. A handy homeowner might tackle easier scenarios, but for more challenging situations a professional installation may be required.