The general procedure for passaging adherent cells is described in the steps below.
Remove the old culture media and rinse cells with a balanced salt solution.
Detach the cells from the bottom of the flask by using EDTA pre warmed  to 37°C, or spraying with balanced salt solution (BSS) and tapping the plate, or through proteolytic enzymes such as Trypsin at concentration 0.025%-0.5%
Prevent clumping of the cells by placing them in a single-cell suspension.  Then, inactivate the cells after harvesting them in a large volume of growth media or BSS+FBS (fetal bovine serum) and centrifuge the cells.
After detaching the cells, suspend them in a small amount of growth medium and perform a cell count using a hemocytometer. Adjust the cell concentration by diluting them to the target density. Then, distribute the cells into new dishes by adding enough medium to allow pipetting 1-2 ml into each dish. Gently swirl the dishes to evenly spread the cells through it. Lastly, seed a known amount of cell suspension into a new culture and carry out microscopic visualization.