Press the Win+R keys on your keyboard, type diskmgmt.msc and press Enter.
In the lower part of the disk management window, locate your USB flash drive, right-click on one of the sections and select the “Delete volume” menu item. Repeat this for the remaining volumes (you can’t delete only the last volume and then expand the previous one).
When there is only one unallocated space left on the drive, right-click on it and select the "Create a simple volume" menu item. Next, follow the simple instructions and upon completion of the process you will get one partition that takes up all the free space on your USB drive.
Removing partitions on a USB drive using the diskpart console program
Press the Win+R keys on your keyboard, type diskpart and press Enter. After that, in order, enter the following commands, pressing Enter after each of them:
In the list of disks, find your flash drive, we need its number. Do not confuse with other drives!
select disk N (where N is the flash drive number)
clean (the command will delete all partitions on a flash drive)
create partition primary
select partition 1
format fs = fat32 quick
On this, all actions to delete partitions on the USB flash drive are completed, one partition is created and the drive is assigned with a letter - you can use the full available memory on USB.