Hi @Anil9860 the storage size is declared in the configs/beaglebone* files using the variable name MENDER_STORAGE_TOTAL_SIZE_MB. For SDCard it defaults to 8192MB and for eMMC it is 3648MB.
Note that eMMC size is limited by your hardware. I’m not sure if there are options of different eMMC sizes or if they are all 3648 which is what my board has.
You can edit those files directly to change the amount of space. Note that number is the total amount of space, accounting for all the partitions. See https://docs.mender.io/2.1/devices/yocto-project/partition-configuration for more details.
Also, you cannot change the partition size in an OTA update. If you need to change the partition sizes, you need to reprovision your board using SDIMG file directly.