The car still needs maintenance, you hear people say "don't re-wax", but in reality it is a good idea to apply a sealant designed for a coating once or twice a year to keep it at its best and well protected. A general rule of thumb I follow is to use a different removal process depending on the type of coating used, the duration of the application and the product you plan to apply once the old one has been removed. However, tile removal also depends on your comfort level and experience with medium to advanced paint correction techniques. In this case, the current condition or longevity of the tile will determine the removal steps you will need to follow.
As explained above, DIY nano-ceramic coatings are intended to provide a semi-permanent layer of protection, which means that they will eventually wear off. Whether you go back to car wax or switch to a professional-grade ceramic, the first logical step is to remove the oldest coating. With any other option, there is a risk that the clear coat will deteriorate or that thicker areas will be lost. Adhering dirt is a sign of surface stress, not the coating itself (unless, of course, the coating is still curing).
At this point in its life, the coating is likely to be very thin and relatively easy to remove. When I removed the cover and took it out of the garage a few weeks ago, I noticed a hand-sized patch in the centre of the bonnet that doesn't appear to have been coated. It also depends on the surface, whether it's the car body, glass, plastic trim or wherever it's applied. As you may already know, ceramic coating is one of the best paint protectors for your car, RV, boat or even aircraft.
Most professional detailers swear by the use of a polishing compound and orbital polishers as the best way to remove a newer ceramic coating. Since the coating will be there on your vehicle for many years, it is recommended to make sure you are coating a near perfect paint job. However, the problem with this method is that it requires experience with polishing and knowing when the ceramic coating has been cut, and not too deep into the clear coat.