How often can I change my ads?

Just a couple questions..

[Lysandra90]

1. Is there a limit to how many times I can change my ads? I put up a skyscraper yesterday but I want to change it to a square.

2. How many ads can I have on one page?

[LifeinAsia]

1) You can change your ads as often as you want.

2) Up to 3 ad units on a page.

[Lysandra90]

Thank you!