As I read your question, you are asking about checkboxes  from the "Forms"
toolbar and not the "Controls" toolbar.

To rename checkboxes that are on a worksheet from the Forms toolbar . . .
- select the checkbox  on the worksheet by Ctrl+click with mouse
- when the checkbox is active or selected, click on the Name box on the
Formula bar and type a new name
- hit enter or click outside the name box
I usually use a naming  convention for checkboxes like cbMyName, where MyName
is descriptive of the checkbox.