Using Partition Wizard on the fly doesn't always work -- sometimes you'll get a message - insufficient memory -- and in any case if it DOES get hosed up you've lost data so ALWAYS backup FIRST -- and this is my EASY method.
EASY way but you need an external device to save data to or a second internal HDD.
1) create bootable media of "imaging backup software" I use Acronis
2) create bootable media of GPARTED or FREE PARTITION WIZARD -- your choicef Partition wizard -- you can download the Partition wizard .iso file and even make a bootable USB stick of it if you prefer.
3) backup entire disk as an image using something like acronis to an external HDD - use high compression.
4) boot GPARTED / Free partion wizard to re-partition your disk with the sizes you want.
5) boot the backup software media you made in step 1
6) restore partition images you made in step 3 but use the new sizes.
Ensure the C partition is set to ACTIVE unless you have the small system partition of 100MB which should be set to active -- if this partition exists then in step 4 you need to make 3 partitions.
7) boot new system -- if it DOES fail -- unlikely but it IS possible just boot the W7 recovery disk and it will fix any boot problems -- you migght have to re-boot 2 or 3 times.
I've done this LOADS of times without fail.