Question: Selecting and replacing the elements of a matrix >20

I have an 8*5 matrix, and i'd like to replace elements of it that are >20 with 20. For those interestedm, the matrix comes from this question.

M := Matrix(8, 5, {(1, 1) = 1.266, (1, 2) = .734, (1, 3) = .656, (1, 4) = .735, (1, 5) = 1.843, (2, 1) = 2.859, (2, 2) = 5.625, (2, 3) = 5.188, (2, 4) = 5.453, (2, 5) = 10.765, (3, 1) = 3.281, (3, 2) = 9.000, (3, 3) = 5.516, (3, 4) = 5.828, (3, 5) = 6.156, (4, 1) = 7.718, (4, 2) = 34.125, (4, 3) = 5.453, (4, 4) = 5.344, (4, 5) = 5.453, (5, 1) = 8.703, (5, 2) = 6.515, (5, 3) = 6.125, (5, 4) = 6.641, (5, 5) = 6.734, (6, 1) = 17.766, (6, 2) = 8.578, (6, 3) = 8.765, (6, 4) = 9.875, (6, 5) = 32.610, (7, 1) = 22.156, (7, 2) = 15.640, (7, 3) = 15.610, (7, 4) = 15.187, (7, 5) = 23.735, (8, 1) = 20.140, (8, 2) = 20.156, (8, 3) = 20.266, (8, 4) = 19.344, (8, 5) = 21.078})

I tried to create a logical matrix that i could input into M (this is how it works in maple) to select the elements so i could replace  them, but this didn't work