Complex sentence: Members are divided into Red, Silver and Gold tiers, with members able to upgrade by accumulating tier points, These are used to calculate the member's eligibility for membership renewal, upgrade or downgrade during the membership year.
Split into simpler sentences: Members are divided into Red, Silver and Gold status, with members able to upgrade status'by accumulating tier points. Tier points are are used to calculate the member's eligibility for membership renewal, upgrade or downgrade during the membership year.