Switching prefabs, what is an efficient way?

Hi, I'm making a 3d tower defense game. The towers and enemy movement are all grid based so I'm setting it up with a tile map.

When I create the tile map, the tiles store the coordinates x and y in the map and if is walkable for path finding.

Based on what the player does each tile could contain a prefab tower, which has the model, what kind of shots and range etc.

Do I instantiate a new tower prefab and destroy the last, every time one is placed upgraded? or is there a way that's less expensive?

Maybe its not as expensive as i think it it, but it seems like every time i make one tile i would load every type of prefab it could be and then just switching between them as the game goes on, rather than just preloading all possible tower prefabs and just grabbing the one the tile needs at the time.