Increase the height of my handlebars to reduce back pain
You need either a shorter (stem)[https://bicycles.stackexchange.com/a/270/19705]  (brings the bars closer) or to raise the stem.

The age given strongly suggests its a quill stem, and will look like this on the inside.



Back off the clamp bolt  (may be a hex socket or a bolt head) a couple of turns, and then gently tap down on the top of the bolt to loosen the clamp down inside your head tube.   Don't undo it fully unless its seized with rust and you have to get grumpy.

Once loose, pull the stem up a bit and retighten.  Go for a test ride and see how it feels.   

WARNING Be mindful of the minimum insertion marks and obey them.   

Once you're happy, tighten up the clamp bolt properly after checking the stem and front wheel are in line.  Use a ruler - don't just eyeball it.   Also avoid overtightening the clamp bolt.

If adding height doesn't help, you'll need a shorter stem, or possibly bars with a little more swept-back and some more uplift.  This starts costing money though.