I will be traveling to Shanghai and staying for 4 days. My passport is from Brazil

If you're not in transit to a third country, then yes, you need a tourist visa.

If your tickets are not yet paid..

You should visit another country after those days in Shanghai to avoid to pay for a visa. If fact, the visa is good for at 6 complete days. Ex: if you land in China on April 4 then you can leave on the 10.

Very important: no transit at all in China. Here You have to land directly in China and leave to another country without any transit inside mainland China.