After generating the Income Statement report, under Cost of Sales you can double click the listed accounts, that will bring up the journal section where the expenses were entered, there you can double click them to edit them.
On that report, the Income is the amount of profits you have had during the selected period of time.
The Cost of Sales is the amount that you have expended in suppliers.
The Gross Profit is the Income minus the Cost of Sales.
Also, check on the chart of accounts that the subclass of the account you use for expenses is not set as an income account, it should be Cost of Sale.