Final answer:
The 'value' attribute is used to change the numbering of items within an ordered list in HTML.
Step-by-step explanation:
The attribute that can be used to change a number within an ordered list in HTML is value. This attribute specifies the starting number of an item in the ordered list. For example, if you have an ordered list and you want to start the numbering from ten instead of one, you can use the value attribute on the first list item (<li>) to achieve this.