Step 1 — record the starting point
Note the current curve number, offset, room temperature, flow temperature and outdoor temperature. Without a baseline you can't assess the effect of a change.
Step 2 — one step at a time
Lower the curve or offset by one step and wait 3–7 days. Compare days with similar outdoor temperature. If the room stays warm, repeat.
Step 3 — find the limit and step back
If the room gets cold or recovery takes too long, raise it back one step. That's your house's optimal point. The estimated saving per degree lowered is 2–3%.
What not to do
Don't change installer-level settings, protection limits, or hysteresis. Don't change several settings at once — then you won't know what caused the effect.