@adido, welcome to the forum!
What you want to achieve should not be too difficult, but a couple of comments first. Since you are wanting to preserve your personal data, back it up before you do anything. Replacing the partition Windows is on with Ubuntu and leaving the other two untouched is fairly straightforward, but any manipulation of partitions involves a slight risk of something going wrong with consequent loss of data. Backup now.
The other comment - your two personal partitions will be formatted either NTFS or FAT32, probably NTFS. Although Ubuntu can read-write NTFS reliably, I advise you not to use this filesystem if you do not have Windows available. NTFS is a Microsoft filesystem and needs the utility chkdsk in the event of filesystem damage. Although there is a Linux utility for fixing NTFS, it is nowhere near as comprehensive as chkdsk.
We need to see exactly what your partition layout is like before recommending something. Boot up your Ubuntu Studio live DVD or live USB (if you have one) and do one of the following. Either open Gparted, the partition editor and take a screenshot of the open window. In Ubuntu you would use the alt+PrintScr key combination for this. I don't know whether this key combo works in Ubuntu Studio as I'm not sure offhand which desktop environment Studio uses. If you can't get a screenshot, open a terminal and post the output of these two commands:
Sorry to throw a couple of terminal commands at you, but this is the easiest and quickest way for getting the information needed. You should be able to copy and paste the terminal output by highlighting it with the mouse and right-clicking -> copy.
sudo fdisk -lu
sudo parted -l
I'm assuming you have an Ubuntu Studio disc already. If not, post back and we'll take it from there.