How do i update a calculated field?

I have a calculated field that needs to updated. Where do I do this?

Apologies, however I am confused on your question. On the screenshot you have provided, that is where you can update the calculation of a field.

However, I noticed you are using brackets and curly braces, please use parenthesis instead, if you want to group the formula.

Also, currently the formula you have added is treated as string by the system, for it be treated as an actual mathematical formula, please click on it so that it's background color changes from brown to black.