replacing fuel filter on a 1986 volvo wagon

No secret, just use good tight fitting wrenches as you certainly don’t want to strip the hexes off the banjo bolts or the filter inlet/outlet. Sometimes it helps to set up your wrenches on the filter and bolt so that you can squeeze the handles together with one hand (like a pair of pliers) and rap on the bolt head with a small hammer - sometimes the shock wave helps the bolt break free. If you already got the front line disconnected, you may be able to get a better hold on the filter by applying a six-point socket to the front of the filter. In extreme cases you can even hold the banjo bolt (let its wrench wedge up against the bottom of the car) and turn the filter with a big long wrench or breaker bar.