TOPIC: Increase the size of description field

I created a custom field but my texts gets cut off on the description field once I save.

How can I increase the text amount in this field. I know it is controlled via the database text size but not sure which table exactly and what field type will need to be changed.

We are using the custom field for our disclaimer on donations as required by law for charity donations and this text must be fully spelt out and cannot be modified or paraphrased.

thanks