How you switch depends on which experience you are using:
Venice Agent (the default experience at venice.ai/chat/agent): you do not need to switch manually. Describe what you want, such as chatting or generating an image, and Venice routes your request to the right model for the task.
Classic Chat (venice.ai/chat/classic): click the current model name in the prompt bar to open the model selector, then choose a text model to chat or an image model to generate images. You can switch at any time without losing your existing conversation.