Fixing water damaged ceiling texture is another common requirement. When the texture loosens from moisture you will need to replace it. Make sure that the underlying drywall is still in good condition. Prepare for a little mess.
Get a drop cloth and a garbage bag. With a scraper remove the loose texture. Texture that is tight should not scrape off easily.
One exception to that. Acoustic texture, the kind with the little balls will come of easily with a scraper even if it is not damaged. Once you have the bad material removed you can think about repairing the texture.
For a discussion on drywall texture repair, go to the article 'How to Texture Drywall'. This article will direct you in how to identify and repair various textures you may have in your home.