Paying debt is the only way to build credit, that is what the system is modeled after.
Create an account with
credit karma or some other free credit monitoring company.
This will give you a good idea what your number is and a list of accounts 2 of the 3 credit bureaus are aware of.
From there you will be able to determine what kind of loans to go looking for to consolidate/refinance.
If the debts are delinquent, you can negotiate a settlement or a new payment plan to pay them off, you can also ask the creditor to remove them from your account after final payment. You can leverage the final payment to get then to comply.
All debts that haven't been paid on in 7 years or that are already paid in full, you can dispute them for accuracy and age, often they will simply remove them.
What range is your credit score right now, and how old are your delinquent accounts?
Other factors for loans include monthly salary, employment record, and other debts.