> I am wandering if Great Snipe change there Lek every year
No, Great snipes are very 'site loyal'. That means when they've set up the lek - they will come there year by year, through dozens of years. But they are very sensitive for any disturbance and when flushed - can easily abandon the lek for years, if not forever... This is what most probably happened to one of the most well known lek on Biebrza Marshes. Luckily, there is couple more lek sites deeper into the marshes, but hardly accessible for humans.
Actually, Great snipes males usually visit couple of lek sites (if present) nearby, during one mating season. Just to maximize their chances to meet a female. Both sexes fly into a proximity of a lek site, about late afternoon and sit still somewhere near in a grass until it's getting dark. Then - if they feel safe - they walk sneaking through the grass to a lek and take positions for displaying. About one hour after sunset the show goes on. Males climb up on tuft of grass, standing up almost on their toes, chests puffed, tails spread in a fan shape, wings lowered and flap the beaks frequently (very odd, weird sound but hardly audible). As the displaying continues, they get so excited that they jump above the sedges, and make short 'parachute' flights and this is for what birders come to ;-)
Late April and turn of May they might start to display earlier, I mean before sunset. On June they may still be on a lek, but hight of a grass and other vegetation is mostly to big to spot the birds, even when they jump. So the game is over about mid-june.