You can replace the existing tables from the restaurant only if you have fixed number of tables per level.
In-order to replace the tables follow the below procedure:
a. Tap on Shop icon located at the left bottom of the screen.
b. Select the Tables icon/ middle icon in the list.
c. Scroll through the different tables and select any one to replace.
d. Once you click on Place, every table in the restaurant will show a box symbol on the top.
e. Choose the one which has to be replaced. The table which has been replaced is now stored in the Shop.
f. The selected table will be replaced in the restaurant.
g. After placing the table in the desired position click on green tick mark.