To replace the brake light bulbs on a VW Polo, pull away the carpeting in the trunk, unscrew the bolt holding the lights on, and disconnect the wiring. Replace the bulbs, put the wiring and bolts back, then replace the carpeting.
A little more information about the layout of the engine would be nice. Beetles that have been modified have all kinds of issues. I had a 1974 super beetle and used to work on a lot of German cars and old VWs in particular. I don't know if you have the original engine in the car. Assuming you have a carburetor it could need to be adjusted to lean the fuel mixture. Also a new air filter may help. You should do all the things any other car would need checked, air pressure in the tires, oil level, tune up. Part of tuning the engine would be adjusting the valves. Also on a beetle you need to be very careful and check for gas leaks. The hose from the gas tank (front of car)to the carburetor (back of car) is notorious for leaking. You could be leaking fuel and if it is leaking near the engine it can catch on fire. Many VWs have caught on fire because of this. So make sure you check for leaking gas. You could be losing a lot of fuel from that or even the fuel tank leaking from rust. The fuel hoses always get old and brittle and leak. It is easy to replace. Good luck!
Just another thought, but I'm in the proccess of replacing my wife's '72 Super's carb and when i took off the stock one it was really dirty on the INSIDE. You might try some carburetor cleaner, that may be enough to set things right. Some times it's the simple things. Just follow the directions on the can. The Beetles are real sensitive on valve adjustments, you can really feel the difference on the power and regained fuel mileage if it been awhile since it was done. At LEAST every other oil change.
There is a Phillips head screw under the plastic cover.
the vw engine code on most models is on the white sticker on the boot floor (sometimes in the spare wheel well). The sticker is a replica of the one on the inside front page of the service book.
On the one litre models it should be checked at 40,000 miles and changed at 60,000 miles or four years. Which ever comes sooner.