If i purchase my tickets for Monday but i want to change the day for Tuesday what I have to do???

Usualy Tickets do not have dates accept for use by dates accept for universal express which is non refundable

As mentioned use it once , on any day

Generally, tickets can be used once anytime.

You usually don't specify the day when you buy a ticket. You but so many-day ticket and you can go anyday(s) you like.