Fresh milk has a pH of 6. When milk changes into curd, the pH value will

Milk is having lactose but after curdling of milk lactose turns to lactic acid
$\underset{\mathrm{milk} \left[\mathrm{Carbohydtate}\right]}{\mathrm{Lactose}}\to \underset{[\mathrm{Acidic} \mathrm{nature}]}{\mathrm{Lactic} \mathrm{acid}}$
Milk → curd
So, pH is going to decrease, from 6.