After purchasing World Creator you are granted to new updates and upgrades for a period of 12 months. Any new release after that period requires you to renew your maintenance plan, else you do not get access to it. If you purchased a perpetual license, you only have access to versions that were released before your purchase and within your maintenance period after purchase, but not to newer versions that were released after your maintenance plan ran out.
Pricing for a maintenance plan renewal is 50% off the current listed price. There is no time limit - you can renew at any time with a total discount of 50%.
Please read this article to see how to renew your maintenance plan. If you renew while your mainetannce plan is still active, the system will add 12 months on top of your current plan.