Hello, as in another thread
(https://forum.fortinet.com/tm.aspx?m=116000) the build 638 is the 5.2.1
build.To upgrade to 5.2.4 build you should check the FortiAP 5.2.4
release notes
(http://docs.fortinet.com/uploaded/files/2532/fortiap-524-release-no...