You will have a bolt on top of the stem. You want to loosen it about 3 turnes and then tap it down with a hammer. You should be able to move the stem up and down then. There will be a minimum insertion mark on the stem so don't raise it to where you can see that mark. Put the bars where you want them and then tighten the bolt.
You probably have a quill stem on this less than desirable bike of yours (I know it has sentimental value to you) . You dont want to raise the handle bar really If it has been 10 years since you first got the bike then Im certain it isnt the handlebars that are too low , it is the entire bike that is now too small for your body!