How to adjust map's tile pixel without affecting the structure of the existing tiles on the map?

I want to adjust the tile size of the map. When I change the tile width and tile height from 64x64 to 16x16 in the map property, the existing tile images/objects on the map shrink and their structure become weird. How to adjust the map pixel without affecting them? I just want to change the map pixel and add some new tiles with smaller pixels(16x16) to the map.
Sorry for my bad English and thank you.

When you shrink the map’s tile size without changing the tileset’s tilesize, the tiles will be displayed on that 16x16 grid, but they’ll still be 64x64 tiles and they’ll stick out of their slots, covering up parts of other tiles. It sounds like what you want is to shrink both the tileset tile size and the map tile size, but replace the existing 64x64 tiles with arrangements of the resulting 16x16 tiles to keep the appearance of those old larger tiles? Tiled cannot do this for you, you would need to rebuild the map with the “new” tiles.

Your tile size should always be the size of the smallest tiles you’ll want to use, and any larger “tiles” would need to be used as multi-tile stamps.