Hello,
In order to be eligible to Upgrade the software (ie. 5.3.x to 5.5.x or 5.7.x is an "Upgrade" and not an Update) on the MSM Controller, you need to have purchased the device on or after the release date of 5.7 (January 3rd, 2012) or have an active Software Carepack registered to the device.
You are also eligible for one year after purchase without a software carepack to software updates for bug fixes. Update in this case means for example 5.5.x to 5.5.x, such as 5.5.3.0 to 5.5.4.0.