should change contact lenses casing often

Do you change your contact lenses casing two or three months time? I never know we should change the casing every three months times. I only think that wearing monthly disposable contact lenses are already safe, but really never know that it is not. My friend told me we should use new casing for each month contact lenses.

Well, I think I better request more casing when purchase contact lenses casing. I hope that they willing to give me with free of charges.