Windows 10: Cannot merge USB partitions

I have a approximate 14.5 GB USB pen drive. Once I had installed an operating system on it, which made its main partition only about 200 MB. Now, I want to remove the installed operating system on that and want to use the whole USB. So I formatted the USB, but again, because the main partition was only about 200 MB, it only formatted the 200 MB partition. And after trying various ways to merge the unallocated space with the partition, I was unable to. No matter what, the "extend partition" option is always unable. At least I am able to make a new partition of the unallocated 14 GB space, but I

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Cant merge Partitions

Hi folks,
i was trying to merge a partition to another one but i couldnt, it said i didnt have GPT or that i dont have enough space to extend it, does anyone know why? there is only 1 unallocated partition im trying to merge into another partition that has files, the idea is to keep the files intact. i tried deleting it then using the extend function but nada. pls help

 

Cant merge Partitions

Move the files, backed up. Use Easeus to delete both partitions, merge, make new parition, and move files back.

 

Partition a USB Flash Drive

USB Partitioning

Do you know the technical part of it? How does the flipping of the removable happen? How can we partition a USB without using a 3rd party software? Can you suggest any programming language? and what algo should I use? thanks!