reduce — to bring down to a smaller extent, size, amount, number, etc.: to reduce one's weight by 10 pounds.
deface — If someone defaces something such as a wall or a notice, they spoil it by writing or drawing things on it.
disfigure — to mar the appearance or beauty of; deform; deface: Our old towns are increasingly disfigured by tasteless new buildings.
mar — to damage or spoil to a certain extent; render less perfect, attractive, useful, etc.; impair or spoil: That billboard mars the view. The holiday was marred by bad weather.
simplify — to make less complex or complicated; make plainer or easier: to simplify a problem.
spoil — to damage severely or harm (something), especially with reference to its excellence, value, usefulness, etc.: The water stain spoiled the painting. Drought spoiled the corn crop.