This can be done (as the various available duplicates will point out) but unless there's been a major development that I haven't yet seen, it's definitely not something for a beginner.
I would suggest a new install from CD/USB alongside your existing Windows installation (proper dual-boot, not Wubi) and after you've copied out all the files you want to keep, you can minimise the space Windows takes up or get rid of it altogether.
I say this for two reasons:
- Installing Ubuntu from scratch takes very little time and has less chance to mess everything up.
- Converting the Wubi soft-partition to a real one and installing a bootloader (which you'll have to if you migrate your Wubi install) is very technical and takes a long time in itself.