If you no longer have need for a schedule C, indicate that you stopped the business in 2017 in the General Info section of your business. This will remove the schedule C and any related schedules/worksheets going forward.
If you had assets for depreciation (vehicles, equipment, etc), you will need to visit the Asset/Depreciation section of your business to 'dispose' of them and stop the depreciation.
If you have only the schedule C to remove, you can also delete the form from your list. Select Tax Tools, Tools, Delete a form. Scroll list for the schedule C to remove.
"If you no longer have need for a schedule C, indicate that you stopped the business in 2017 in the General Info section of your business. This will remove the schedule C and any related schedules/worksheets going forward."
That statement is not all inclusive and can be misleading. When you indicate you stopped the business in 2017, it does not (and should not) remove the SCH C from your 2017 tax return. If you work through the SCH C and correctly show the disposition of all assets, inventory, vehicle use and anything else associated with the business (such as good will) then 2017 will be the last year you will file a SCH C for this specific business. If done completely and correctly, then next year when you start the 2018 tax return and indicate that you did not have a business in 2018, the SCH C stuff will not be imported from the 2017 taxes to the 2018 taxes.
If you indicate on the 2018 taxes that you did not have a business in 2018, and the 2017 SCH C information is imported anyway, that usually indicates that you did not completely report the disposition of the business in it's entirety on the 2017 return. Therefore the IRS considers your business to have been open in 2018.
There is no such thing as a "retired" version of TurboTax.
If 2017 was the last year your business was open, then regardless of what else you may read here, UNDER NO CIRCUMSTANCES WHAT-SO-EVER do you delete the SCH C from your tax return. There are no exceptions. If your business closed, was sold or otherwise disposed of in 2017 then you are required to file a SCH C to show the disposition of your business. This is especially true if your business has depreciable assets, or carries an inventory, or claims any vehicle use for business.
At the start of the business section you select the option to indicate that you sold or otherwise disposed of the business in 2017, then continue working it through "AS IF" you still have the business.
When you get to the "Sale of Assets/Depreciation" section you must work through each individual asset one at a time to show it's disposition. Either you sold the asset, gave it away, removed it from the business for personal use, it was stolen, destroyed, or whatever.
If you claimed any vehicle expenses at any time in any year the business was open, then you must also work through the Vehicle Expenses section and show the disposition of the vehicle also.
If your business carried any inventory, then your End of Year Inventory balance *MUST* be zero. If it's not zero, then simply indicate that you removed all remaining inventory for personal use, and that will make your EOY Inventory Balance zero.
As far as the IRS is concerned, until you have completed all the above in it's entirety, you are still in business and they will be expecting a SCH C from you the next tax year also.