Take a look at the stitch in the sweater and if you are not sure ask your local yarn shop. If you try to unravel a machine-knitted sweater you will find out very quickly that you have a problem.
First you need a pair of scissors with small tips, ones that are often used in sewing. Use these scissors to trim the seams that hold the pieces of the sweater together. Look carefully, don't just cut with large scissors or you will encounter problems. Find the seam, separate the seam to find each side of the two pieces sewn together and cut only the stitch you see running between holding the two pieces together.
Cut each of the seams, then you can start to unravel. Or work in stages if you prefer. Unraveling will take a bit of time, but it's great if you are watching your favorite show or you happen to take a bus/train to work.
Don't be surprised if occasionally a yarn breaks, but if you are careful this shouldn't happen (maybe only twice!).
Now I have this stack of yarn that I need to soak to straighten it then I can spin it into a ball for my intended project.
|Here's the buttons I saved.|
|One seam cut - sweater is in two pieces|
|See the two pieces?|
|1 sleeve and the yarn from one side of the body|
|Here's the seam before separating and cutting|
|The other side of the sweater|
|Lots of yarn|
|Here's all of the yarn|