sda6 is ext4 file system and where my ubuntu is installed, 30GB. sda3 is "ntfs" file system and where my windows is installed, 400GB. sda7 is a 50 GB empty partition with "ext4" file system.
How to move the space of sda7 to sda6 to let sda6 become 50+28=78 GB.
Here's a real case of mine :( I want to add more space into my ubuntu (28.2 GB one) from other emtpy partition space.
Make sure that you have a good backup of your important Ubuntu files, as this procedure can corrupt or loose data.
Keep these things in mind:
always start the entire procedure with issuing a swapoff on any mounted swap partitions, and end the entire procedure with issuing a swapon on that same swap partition
a move is done by pointing the mouse pointer at the center of a partition and dragging it left/right with the hand cursor
a resize is done by dragging the left/right side of a partition to the left/right with the directional arrow cursor
if any partition can't be moved/resized graphically, you may have to manually enter the specific required numeric data (don't do this unless I instruct you to)
you begin any move/resize by right-clicking on the partition in the lower pane of the main window, and selecting the desired action from the popup menu, then finishing that action in the new move/resize window
Do the following...
Note: if the procedure doesn't work exactly as I outline, STOP immediately and DO NOT continue.
gparted
Follow these steps to get things done:
Detailed procedure of partitioning can be found in this question How to resize partitions?
Alternatively you can let sda7 be separate partition and move your /home to that. You might like to read How to create a separate home partition after installing Ubuntu under single / partition.
I believe B is in between A and C. Although you can merge C and D but it is impossible to merge A and C, since partitions need to be in contiguous form to be extended or merged or you can say, partitions need to be exactly above or below the unallocated space to get resized. Moreover unlike Windows Ubuntu can't work on dynamic disks, so it is impossible to extend the partition using the partition which is very far. So it is better to merge C and D (and have 65 GB) and keep partition A as a separate partition.
If you really want only one Linux partition as you say:
Backup all important data from all your disk (Ubuntu, Windows and all other partition) - or take the risk of losing them. There is also some risk to get in bigger trouble with the HDD altogether when partitioning, but life is risky..
A system partition cannot be modified while in use, you have to put Ubuntu on a live usb stick (use Etcher or Gnome Disks to create that)
and boot from it. If you have already an Ubuntu iso you can put that on the stick, if not, download it, or maybe a version with a smaller iso (Xubuntu etc) that has gparted included. If it's not included (rare case) you can install it even there if you connect to the internet in the live usb session and run sudo apt install gparted.
While booting from live usb (restart pc with the usb attached, you might or might not need some bios setting and/or pressing a key like Esc , F8, F9, depends on the machine - some details here): delete the sda7 partition to create a free space, then select sda6, select Resize/Move drag the sda6 to the left.
Extending to the left is in fact moving a partition - and that can take much more time than when simple extending a partition (to the right), so be sure you have power supply during procedures.
