If you're a registered user, your MemberTies license entitles you to install all new releases throughout a "Free Update" period. This is typically one year from the date the license was issued or last renewed.
Each MemberTies release has an "Effective Date". If your Free Update period ended prior to this date, you will need to renew your license (at a discount) in order to use the new release. Once you renew, you'll receive a new license with an extended Free Update period.
To check the date for your license in MemberTies, choose Help > About MemberTies from the menu. On the License Info tab, look for the date labelled "Free Updates Until" as illustrated below. If the date has passed, or your version is old enough that it does not include a date, you will need to purchase a license renewal.
Identifying the Free Update period of a license.