Hi J.,
I used to work alot with a credit reporting company, and paying off a negative item SHOULD NOT lower your score. It might not raise it right away, but it should not lower it. A couple of suggestions:
1) Pay off the debt. The sooner you do, the sooner it will be off your credit history.
2) Call the company with whom you have the collection item - explain to them that you would like to pay the item in full, and see if they will work with you to get it off your report. Some companies will do this if they get payment in full. Even if they aren't willing to take it off, get a letter from them stating it has been paid and the date it was paid. They sometimes take a long time to report it to the credit bureaus, and having a letter in your possession will only make life easier for you should you want to obtain new credit.
3) Make sure you get the name of the person you spoke to (first and last) and the date, time and department if applicable. Also, make sure to ask them if they have a direct # or extension, so that you can call them back directly if necessary instead of talking to someone new.
4) Sometimes, the person you talk to isn't always willing or able to help, so don't be afraid to ask for a manager or supervisor.
5) Keep a copy of EVERYTHING!! Your payment, documentation, etc.
Also, to help your credit score go up, close any cards that you don't use. Open credit cards or credit lines, even without balances, tend to keep a score lower. And if you have to use a credit card, try to pay it off in full at the end of the month (so hard I know...but this does show credit responsibility and does raise your score, even if you only charge $50/month).
I hope this helps, and good luck!