A common confusion here is that people will often use the term DTI when they mean Total Revolving Utilization. If we replace those two terms in our OP's original question, it instantly makes a lot of sense.
OP, are you planning to buy a house in the next couple months? That's where DTI comes in most often. As others have explained, FICO scores are based solely on what is in your credit report, and since the report does not contain income, DTI is not a part of FICO.
If you are sure that DTI is what you are asking about, then I suggest you do some more research out on the internet. Lots of good articles that will walk you through that. As the other have explained, DTI has nothing to do with size of CC limits, and only with the amounts you are required each month to pay on cards, loans, and a few other obligations (e.g. rent or mortgage). Those obligations are totalled up and compared with your monthly income (I believe it is gross). The ratio becomes your DTI. Mortgage lenders are very interested in both your FICO mortgage scores and your DTI.
