How can I globally change a category name?

Are you referring to changing category to all banking transactions downloaded, crosbydesai?

If so, you can do this by creating a bank rule. This will help you categorize all downloaded transactions involved automatically. Here's How:

1. Go to Banking from the left menu. 
2. Select the Rules tab. 
3. Click New rule.  

Take a look at this article for additional details: Bank rules. 

Please let me know in the comments below if you're referring to something else. I'm more than willing to help you anytime.

I have just started a new business in quick books. I have called a category "purchase of fruit and veg" I want to call it "purchase of veg." How can I change this please.

Richard