Every time if you want to add or subtract something to existing value you have do put that value first.
if you eant to change opacity over time you can't put:
Set opacity to +1
You have to do:
Sprite: Set opacity to Sprite.opacity+1 (it says - current opacity value +1)
same for size, speed, position etc.
and make sure you use time delta to change value over time with the same speed for faster and lower framerates
Sprite: Set opacity to Sprite.opacity+1*dt - it will add 1 to current opacity every 1 second
You can use "self" instead of instance name
Sprite: Set opacity to self.opacity+1*dt
ps. i have no idea why i used opacity in that examples ;)