Upgrading an XL4 to an XL4 Plus involves upgrading the Q04 processor firmware to Q04 Plus.
This application note guides you through the upgrade procedure.
Once upgraded, subsequent firmware updates are via USB as per the XL4 Plus RTU.
In most cases an XL4 Plus RTU can be directly substituted for an XL4 RTU.
However, there are some exceptions where changes are needed to take advantage of all the new features, such as Modbus Slave and Extended Point Count. This supplementary guide outlines these, please contact techsupport for more information.