Also worth getting some desolder wick/braid. I've found 3mm (wide, it comes in various widths) works well for that sort of job. Mike used it when he did his MP1 pots (much the same job) and it worked well, seemed to me better than a solder sucker for that kind of desolder (ie fair bit of solder and flat wide lugs). So you put the end of the braid on the solder and heat it from on top of the braid (also dissipates a bit of heat into the braid which will help not to overheat the join). When the solder melts it gets sucked into the braid (you'll see it). Try each flat side of the lug using fresh braid (cut the used end off the braid)
And as MJMP said, if it's being problematic, resolder and then go again (pause to cool down in between so you don't wreck a pad).