@Tanny 

EAP disconnect from the controller indicates that the link between the two is lost. To test the connection between EAPs, use the controller host computer to send ping requests. Furthermore, you should check whether the physical connection of the EAPs to the front end router is working properly.If there is a connection issue, updating firmware will not resolve the disconnect. However, you can still update the firmware of the controller and the EAP225 to more recent firmware because the newer firmware includes more features than the older ones.Compare your current firmware with the latest firmware; there is a significant difference, thus the backup file cannot be uploaded to the latest firmware. I suggest that you reconfigure it after updating it.

Download the Controller firmware from there

Download the EAP225 Outdoor firmware from there