The answer depends on the plan you purchase.
The Value Plan (1 year of support and updates plan) includes upgrades for as long as you maintain the plan. This plan must be renewed yearly to maintain this access to both upgrades and the extension license.
The Lifetime Plan (3 month of support and updates) plan includes upgrades for 3 months.
For example, if you purchase the Value Plan for 1 year, you will get upgrades any time during that year. If you do not purchase a new plan at the end of the year (either a Value or Lifetime Plan), then you will no longer receive any upgrades.
To learn more about licensing, see our article "Understanding Extendware Licensing".