If you'd like to change or delete a group of tiles (and not your entire tile installation), you can do this from the 2D WALL or FLOOR windows or from the 3D Navigation window.
2D WALL OR FLOOR
Selecting a group of tiles with a polyline
It is possible to eliminate or substitute a group of tiles with the “Delete Group of Tiles” or “Change Group of Tiles” commands and using a polyline to define the area of selection. These commands are available in the Wall 2D or Floor 2D windows, under the WALL tab of the main ribbon.
Once you've selected the operation you want to perform, an info message will appear to help guide you through the actions to complete:
At this point, you can simply trace a closed polyline to select the group of tiles to delete or change (while drawing, you can use the O key to activate/deactivate orthogonality).
Once the polyline is drawn and closed, all tiles contained within the selected area, even those that are only partially contained, will be included in the selection.
Once the polyline is closed, the selected tiles will be outlined. If desired, it is possible to continue adding to the selection by clicking on individual tiles with the mouse. To end and execute the operation, users must right click on the mouse, which will confirm the end of the selection.
Check out this video tutorial on the feature!
Selecting multiple tiles by clicking
Open the 2D surface window. From the "WALL" tab of the main ribbon, click on "Change Tile -> Change Tile" or "Modify -> Delete" 
After you've activated the command, use the mouse to click on each tile that you want to substitute or delete (they will be outlined in blue after you click on them). Once you've finished selecting the tiles, right click with your mouse to finish and confirm the selection.
In the below example, the darker tiles are those that have been substituted as shown above.
3D NAVIGATION
From the 3D Navigation window, right click on one of the tiles that you'd like to substitute and select "Change Tile -> Multiple Selection", or from the main ribbon click on "Change Tile".
Next, using your mouse, select each tile one-by-one that you want to substitute. Right click to finish and confirm the selection. Then, select the new tile that you want to use to substitute the old tile and leave the replacement type selected as "single tile". The program will then substitute only the tiles that you've selected manually.
This article is valid for the 2022 version and later.