What they all said, plus a reminder that while you're talking about going up a small amount of total weight, the difference is huge as a percentage of what you were lifting before. Don't worry about finishing the same number of reps -- when you go up in weight, expect to do as many as you *can* do, and then build the reps back up from there. (In fact, I'd say that if you were able to knock out the full set at the higher weight, you weren't lifting enough to really train your body before -- this sounds like you're increasing your weights at the right time for you.)