How do you change castforms forms in Pokemon pearl?

To change Castform's form, you need to wait for a specific type of weather to occur. Here is a table showing the weather conditions and their corresponding Castform form:

Weather Condition | Castform Form

------------------ | --------------

Sunny | Sunny Form (sun symbol on its head)

Rainy | Rainy Form (rain symbol on its head)

Snowy | Snowy Form (snow symbol on its head)

You can check the weather conditions by looking at the top right corner of the bottom screen. If the weather is one of the three conditions listed above, Castform will automatically change into its corresponding form.

Please note that Castform can only change its form once per day. If you change the weather multiple times, Castform will not change form again until the next day.