Question

who we can reduce or increase friction

Answer 1

By increasing/decreasing the irregularities on the surface. This can be done by the following-
a. Greasing
b. Using ball bearings
c. Using wheels
d. By designing specific designs which help to reduce friction
Hope you find it useful...

Answer 2

we can reduce friction by putting on oil or greasy things on the substance, where u want to reduce friction. however, water can also be helpful
we can increase friction by rubbing a rough surface over a surface where u want to increase the friction. wearing and tearing of substance also increase friction.
hope its helpful