Finally Diskpart tool in windows came for my help.
Follow the below steps to delete all the partition on your drive and get back the full space to use:
- Open Command Prompt in Administrative mode (elevated mode).
- In the prompt, Type Diskpart
- In the prompt, Type List disk
- Note the disk number that corresponds to your USB drive (it should be obvious going by size)
- select disk X where X is the number from step 4
- In the prompt, Type list partition - There should be two, numbered 0 and 1, each about 7 GB
- In the prompt, Type select partition 0
- In the prompt, Type delete partition
- In the prompt, Type select partition 1
- In the prompt, Type delete partition
- In the prompt, Type create partition primary
- In the prompt, Type exit
- Exit Command Prompt (type exit or just close the window)
- In Windows, go to Computer and try to open the disk. It will ask you to format it.
- Format it with the default settings and give it a name if you want.
- It should now a single, unified partitioned drive.