Answer: Changing the amount of a substance would change its mass and volume.
Explanation: The density of a substance will generally always remain the same. This is because density is measured in unites of g/cm^3 which is a ratio. If you change the amount of the substance the ratio of mass to volume will still remain the same.
For example, let's say a student has a 3g/cm^3 block of iron which weighs 3g and has a volume of 1cm^3. If the student cut he block in half and discarded half of it, the remaining block would now weigh 1.5g and have a volume of 0.5cm^3. This means that the density is now 1.5/0.5 g/cm^ which is equal to 3g/cm^3.