undo the nut or nuts on the side of the chaincase, take off the side cover, pull the bar off the adjuster and push back towards the sprocket, feed the chain on to the bar, adjust the bar adjuster by undoing it until you can get the bar back on then put the side case back on and do the nuts up finger tight and adjust the bar until the chain is free running but a snug fit, lift the bar upwards and do the side cover nuts up.
On thinking about it, not getting this adjustment right could cause serious injury so would suggest you take it to an experienced chainsaw usere/dealer for tuition or repair.
Steve, March 2009