click on your "income" up in the left corner of your empire screen
if the debt is from fleet= >then disband your fleet, becuase you probably forgot that ships have an upkeep cost per turn, other than the initial buying price
then click on income again, if "debt interest" is still holding down your profits, then sell everything you can on the market, then once sold, check again... if at that point you are still in negative income, you must restart your empire, by going to the options menu and choosing, "restart empire"
please keep in mind that you should not spend turns, and none of what i described requires turns, for if you spend turns you will generate more debt
only spend turns once your income is posstive