Ubuntu – Can’t resize partition during installation

You can't resize a partition when you are using it.

So you have to use an Ubuntu Live CD, boot on it, and then do your operations from the Live environment. Eventually, you have to "swap off", that is to say turn the swap partition off by using Gparted.

The Ubuntu partition sda5 is a secondary partition to the primary partition sda4 so you can't resize sda5 beyond the size of sda4

To resize the Ubuntu partition, you must first resize sda4 by extending it into the free space you have created. Then the next step is to extend sda5 to use up the extra spaces in sda4. You can do this in gparted and apply the change in one go.

Here are the steps:

1. Move the sda3 partition so that the free space is after sda3 (not before it like it is shown now).
2. Resize sda4 into the free space before it (by extending sda4). Be sure not to select sda5 by mistake as it is just an outline surrounding sda5.
3. Lastly, resize sda5 to fill up the larger sda4 partition you have created.
4. Now, apply the changes.

Good luck.

PS: Should backup important stuff in case things go wrong.