Usually, on the bottom limb, there is a sticker or some sort of marking with a Serial #, draw weight, draw length, etc... This will give you a rough idea of how much weight the bow is capable of.

While it doesn't solve your problem, it at least gives you an idea.

If there is no sticker, or it doesn't tell you what you want to know, you can always turn both limb bolts until they are tight, alternating 1/2 turn or so on each one. I would NOT turn one all the way in, then the other. Alternate. Once they are tight, most bows allow for around 4 turns out of the limb bolts. Again, alternating which bolt, turn them out a total of four turns each in 1/2 turn increments. This should now have the bow set at it's lowest setting.

If the bow is still too hard to pull back, or the draw length is not right, you'll probably be better off selling it and finding a used bow that fits you better.

Even better than the above -- take it to a pro shop, tell them you got it on trade, and ask them if it can be made to work for you. But be sure you find a good pro shop -- not Bass Pro or Gander Mtn (at least from my experience).

Good luck and happy shooting!