In fact, there are several people asking about how to fix this issue. Facebook has a guide over here. But some of you might still find it confusing.
The first tip is click Settings at the top of your Page.
When it says "your page" means the name of your site. You can see it on the blue bar or band on top of the screen. It is next to the word "Home".
In fact you can click on the name of your site or even Home to change the category.
1. If you click Home, then the next thing you you need to do is to click on Edit Page.
2. The words Edit Page are on top of the left hand corner, right under the name of your site.
3. Similarly, you can just click on the name of your site which is on the blue bar on top of your Facebook page, as mentioned above.
4. Either way will lead you to the same page where you need to click on the word "Settings" which is on top left hand side of the page.
5. It will open another new page, click on Page Info which is listed on the left side of the page.
6. Now you can see the word "Category" among other options listed on the right side of the page.
7. To change the category, click on the word "Edit" which is on the right side of the page.
5. After you have make your changes, click the Save Changes button.
6. That's all.