Mix the yogurt and sugar together so that there are no lumps in them. Then add the frozen berries. If you want popsicles, pour the mixture into ice cream molds and insert a stick into each one. Place the molds in the freezer for at least 3 hours. If you prefer to have ice cream, fill the mixture into an ice cream machine and process it according to its instructions, or put the mixture in a Tupperware container or something similar and place it in the freezer compartment. Without an ice cream maker, stir the mixture every half an hour. A couple of hours later, your ice cream will be ready.