Problem resizing a dynamic VDI HardDisk

[Moracle]

Hi all,
First newbie question. Sorry if trivial...
I created my first VB (Win 7 64, hosted on the same OS) with a 40 GB dynamic VDI HD.
I runs well but the HD is now full, so I tried to resize it to 130GB using the VBoxManage modifyhd xxx.vdi --resize 130 command. It seems to have succeeded, the VB storage settings shows now a Virtual Size: 126.95 GB and Actual Size: 35.63GB, but when the VB machine is launched, Windows always shows a system disk c: limited to 40GB !
What's the problem ?
Thanks for your help.
Hope it will not require a Moracle...

[mpack]

Resizing a disk does not change the size of the partitions already put on the disk by a guest OS. You need to use a guest tool to change the guest partition size. For a Win7 installation, Google for "DiskPart", and make sure the instructions you follow are specific to Win7.

[Nasuno]

If in windows 7 you can just use the built in "disk management" that comes with the OS.