If you come from more far away, and you wanna Fly, the next bigger Airports are Malmö and Kopenhagen. But there is also a very small in ??? ??km away from Sölvesborg.
The best would be Kopenhagen, from there you find easy the Train to Malmö and Sölvesborg. (The Train Station is under the Airport)
Train is also no problem, including you come from deep south(I meet people from Greece and Spain on the Festival!), and it's maybe cheaper.
If you wanna go by Bus, the People from the Festival organize spezial Bus transfers directly to the Festival from a lot of places. Take a look to the Swedenrock Festival Page.
Also the Car is a possibility, but don't forget - the Police is definitly controlling after the Festival.
There is a big Parking Place beside the Festival.
It's not allowed to bring the Car to the Tent, but there is an extra Camping for Caravans, to this place you can bring your Car.
One more posibillity is the Motorcycle, there is an extra Camping Place for Biker, so you can take the Bike with you.