I always tell the students, if you want to keep track of something, you need to make a variable to do so.
In this case, it seems as though you need to keep track of whether the score has increased by two.
So you could make a var that is called deltaScore and set it to zero. (before the draw function)
You need to find the place where the score variable gets changed and changed deltaScore every time the score changes as well.
Then you could write an if statement inside the draw function like
if( deltaScore == 2)
sprite.velocityX += 0.25 ;
sprite.velocityY += 0.25 ;
//And then it is key here to reset deltaScore to zero so that the process can start all over again.
deltaScore = 0 ;
Let us know how it goes.