Breezeline Stream TV is designed to adapt its picture quality to your WiFi connection. Start by making sure your Stream TV Box is located where it can receive a good WiFi signal. Also, make sure your Stream TV Box detects your TV’s resolution correctly. You can change the resolution under Menu > Settings > Device Settings > Device Preferences > Display > Screen Resolution.
If that doesn’t resolve this, you can get a better reception by using an ethernet cable instead of WiFi. Simply connect an ethernet cable to the back of the Stream TV Box on one end, and to your gateway on the other end.