Deleting negative account or any other negative information from the credit report is not likely to influence your credit score immediately. First of all you need to consider the fact that apart from negative information credit scoring model also considers the stability of the information being reported to the credit bureau. Whenever a negative information is taken off the credit report the credit score does not adjust itself immediately in spite of the fact that the removal of the negative data is a positive process. It is not immediately apparent whether the change in the credit report is a positive one or not. For this reason the credits scoring model will take a certain amount of time in which it is clear that the changes that occur in the credit history was a positive one before making the necessary change in the credit score.
Another thing you need to seize whether there is other negative data being reported on your credit history such as league accounts, court judgements on bankruptcy. The more severe that nature of the negative information being present on your credit report even though it may be from some time in the past, the less influence will deleting a single negative item from your credit history make on your credit score.