A: This can be affected by two different settings. Check membership rules for their current offering in the membership template. The time limits for specific actions are set there, and depending on how long it's been since they purchased their membership, they may be restricted in what actions they are eligible for.
Also check the Upgrade/Downgrade rules, which set what membership levels can be upgraded or downgraded to. Check the Rules section in Memberships, and click on the "Upgrade/Downgrade" tab. This will determine for each level, what memberships that can upgrade or downgrade to. If an integration with Raiser's Edge is in place and the rules for upgrade/downgrade indicate that the member should be allowed to do so, contact your Client Services Manager for more information.