How Can I fix terrible without going through a credit repair agency?

I need serious help! I am thinking about going to a credit repairing agency. My credit is terrible. And I really want to fix it. I don't have any credit card debt but almost everything else is on there. I want to set up payment plans and consolidate. How can I get the lowest monthly payments from the companies? Also, the debt I already paid is still showing up as my negative items on my report. How can I get the companies to put the items positive? Also, It's an unlawful detainer on my credit from an apartment. But I was never served any court papers and I moved out wayyy before. (thats another story!) It's saying I owe them $2,000. My question is, if I pay them the money just to get it over with, Can I get the unlawful detainer removed from my credit? So do I need to go with a credit repairing agency(if so, which one) or is it possible for me to fix my credit myself? Thanks for the help, it's well appreciated!