Two different limits are involved. The context window is how much text the model can consider in one conversation, including your messages, its replies and pasted documents. Saved memory is a separate store of facts about you that carries across chats. When either fills up, quality drops or you see errors.
For a full context, ask the AI to summarise decisions, open questions and key facts, then paste that summary into a new chat. Avoid pasting whole documents repeatedly; share only the relevant sections. For full memory, open the settings, delete outdated items and merge duplicates. Keep one project per topic so each chat stays focused. Exact limits vary by tool and plan, so check the current docs.