If I understood your question correctly I think you were asking about lowering your credit limit, which you shouldn't do. Instead you want to lower the ratio of amount owing versus the credit limit of the card.
For example:
If you have a credit card with a $10,000 credit limit and the balance of the card is at $7,000 then this will impact your credit score negatively because your balance is 70%....it indicates you maybe relying on your card to supplement income.
Ideally you want your balance on your cards to be no more than 30%, but if you can keep them at 10% or lower that is the best scenario for your credit score.
I've recently been through this and have watched my credit score jump by paying down what was a high balance. (I started at 585 at the end of December and it has gone up to 640 by January 20th from paying down my balances....yes they were high, and yes I did pay down quite a bit, but that is a substantial jump in my score.
Also, I don't agree with patti45 about only keeping one card. Any cards that you close now will have a negative impact on your score because you are closing an older account. One of the factors that makes up your credit score involves the age of accounts....the older the better. In addition another factor that helps to determine your credit score is the type of accounts you have. They want to see that you are responsible at handling different types of credit so a mix of Instalment accounts and revolving credit helps boost a score as well.