The chmod command allows to add (+) or remove (-) the rights (r,w,x) to the owner (u), group (g), others (o) or all (a).

chmod u+x ./run  : the owner can execute
chmod g-x ./run  : the group can't execute
chmod o+r ./run  : others can read
chmod a+w ./run  : all can write in the file

Values of x,r,w can be set in binary form.

r=4, w=2, x=1 

rwx = 4+2+1 = 7
r-x = 4+0+1 = 5
r-- = 4+0+0 = 4

rwxrx-r-- = 764
chmod 764 readme.txt