Most drill press quill return spring adjustments are based on the same principles, although the design details may vary. So, what follows is a very general description.
Basically, there is a clock spring contained inside some sort of metal cup. This metal cup is usually kept in place by means of two nuts, and has several notches. On the drill press body there is some sort of nipple, where one of the notches of the metal cup may engage. By slightly and very carefully releasing the nuts the cup may be lifted - careful, if you let the spring unwind bad things may happen - the notch disengaged, the cup is rotated in the desired sense (wind or un-wind, so the spring action becomes stronger or lighter) and the following notch is engaged on the nipple. Then tighten the nuts again - not too tight, there is a nut and a counter-nut for a reason - and it is done. If the backing action is not strong enough, just repeat the process.
I strongly advise you to wear work gloves during the proceedings - otherwise, if the spring unwinds suddenly, you may be in for a nasty cut in a hand.
Of course, it may happen that the spring in your DP is broken, in which case it will have to be replaced, or that the quill is dirty/rusty.
I don't know how experienced you are in things mechanical. it might be wise to study first the manuals of some DP you may find in the net, so you may become somewhat acquainted with the principles of adjusting the return spring. Just google "drill press return spring adjustment", or look into these:
http://www.micro-machine-shop.com/Jet_J ... manual.pdf
http://www4.uwm.edu/letsci/psychology/f ... P15501.pdf
http://www-personal.umich.edu/~jfarrugi ... 7Drill.pdf
A little confusing maybe, but I hope to be of help.
