Replacing 2 Big IP units

Hi Seth, thank you for your answer. actually i tried to import the ucs file took from a device with 10.0.0 to a device with 11.5 without the license but it gave an error and the import failed. also i was planning to use the SCF file from the device with 10.0.0 and make the necessary changes and trying to put into the device with OS 11.5 and check. if it didn't work fine, my last step is to disable the HA between the devices running OS 10.0.0 and try to upgrade the secondary device into OS 11.5 and then i will take the configuration (either UCS or SCF) and copying it to the new devices. do you think that is there any other method we can replace the appliances other than that?again thank you for your help.