How do you find a single number or name you want in a large worksheet containing thousands of numbers and
names? Is it possible to replace a name or number with
some other name or number? How?

The answer to this question is given below in the explanation section.

Explanation:

You can find a single number or name in a large worksheet containing thousands of numbers and names using the find and replacement feature in excel.

You can use Ctrl+F keyboard shortcut for finding and replacing features. When you press Ctrl+F, a dialog will get open, using this dialog, you can find the required number or name while entering in the search text box. Then, click on the Find button, if the worksheet matches the result, give you the matched result in the yellow highlighted color.

Also, you can use Ctrl+F to replace a name or number with some other name or number.

Alternatively, you can do this using the home tab, then find the option find and select under the editing group of commands.