It depends on the collection agency and how they'll work with you.
Some collection agencies will remove the collections from your credit report after you pay them off and some will not.
Before paying off a collection account contact the collection agency and ask them if they will remove the unpaid collection remark from your credit report if you do pay them off.
If they say yes then pay the collection off but if they say no then don't pay them off because it won't do any good for your credit report or credit score.
The collection will eventually be removed after 7 to 8 years anyway.
You may also have to contact a credit repair agency and pay a fee to have them help repair your credit and improve your credit score faster.
Another way to raise your credit score is to apply for a secured credit card where if approved you put up a deposit and that deposit will be used as your credit limit.
You then use the credit card like a normal credit card and pay the bill off and when you do make on time payments and are responsible with the secured credit card the secured credit card will help to slowly raise your credit score and then you can eventually get approved for a normal credit card and other loans that can help rebuild your credit.