[PROBLEM] Resize partition after xbian installation

[Pascal]

Hi,

My Xbian system (20150218-1) was almost full (4G sd card).
I used xbian cleaner to empty thumbnails dir (had to repair the btrfs partition after to free empty space)
Now I have a new 8G sd card where I put an image of the 4G sd card system.
The system boots but doesn't use all free space of the 8G sd card.

Terminal

xbian@arwen ~ $ sudo fdisk -l

Disk /dev/mmcblk0: 7.5 GiB, 8068792320 bytes, 15759360 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0x982fedaf

Device Boot Start End Sectors Size Id Type
/dev/mmcblk0p1 * 2048 71679 69632 34M b W95 FAT32
/dev/mmcblk0p2 141312 7241727 7100416 3.4G 83 Linux
/dev/mmcblk0p3 7241728 7744511 502784 245.5M 82 Linux swap / Solaris

Disk /dev/sda: 3.7 GiB, 4004511744 bytes, 7821312 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0x982fedaf

Terminal

xbian@arwen ~ $ sudo btrfs filesystem df /
Data, single: total=3.01GiB, used=2.14GiB
System, single: total=4.00MiB, used=16.00KiB
Metadata, single: total=376.00MiB, used=49.66MiB

I red on the forum that xbian autoresize the btrfs partition at boot time, and if it doesn't work, the best is to use Gparted.
So I boot an ubuntu on a mac but Gparted doesn't see free space after the swap partition.
Disk utility is able to see the last 4G but doesn't seem to be able to do something.

Any idea to transfer easily my 4G xbian on the 8G sd card and use all space available ?

Thanks
Pascal