Although it is a cheese, ricotta does not last as long once opened as its harder siblings, such as parmesan or cheddar, yet it will still be good to use again in a week.
Soft cheeses like ricotta should last around one week after opening, according to the USDA — that's provided you're storing it between 35 and 40 degrees Fahrenheit in the fridge.
Some sources suggest that ricotta may last up to two weeks, but past that one-week mark you should look for signs of spoilage. If it's more than two weeks, throw it away.