Enter the cost of the new windows as Assets in the rental section of your return under Wages & Income/Rental Properties and Royalties (Sch E). In the Rental Summary, choose "Start" next to Sale of Property/ Depreciation (see screenshot below) Answer the questions on the next few screens until you reach "Did you make improvements to XXXXXX in 2018?" and answer "Yes". Follow the remaining program prompts to complete your entry.