You appear to have two options. You can either `clone` the drive on which you have Windows to another drive, or, you can `recover` your backed up windows to the drve you want to use as your boot drive - but you must ensure the drive is bootable and is your `System` drive.
I would clone C: to G: for ease and speed. Cloning will leave Windows on your C: drive and you will simply need to change the boot from C: to G: and rename if necessary. If I remember correctly Acronis provides you with the option of changing your boot drive after cloning. You can check this out fully in the Acronis Help file.
Having changed you boot drive you will need to format the old C:.
One further point; ensure you have an Acronis Emergency Disk available to be able to use the backup if you suffer some sort of problem/failure during the process.