Sticking to walls is a problem mentioned in this Unity learning module around 8:45, and they set the friction of the ground to zero to solve it. However, they don't address the sliding down slopes problem.
Option 1: your link to the asset is just taking me to the store. But ifGive the uppercharacter's body has a rectangularfrictionless rectangle collider, make it slightly that is just wider than the circle collider and give it a friction of zero rather thanat it's feet, with its bottom positioned half way up the ground having low frictioncircle collider. The rectangle will hit the wall instead of the feet, and the character will slide right down. If it doesn't have You could do 2 angled plane colliders instead of a rectangle collider, you could just add a small one on either side of the player, or maybe an 2as a rectangle collider's bottom corners could get caught on the ground when falling off cliffs - angled plane collidersplanes wouldn't if you want it to work for steep slopes toopositioned well.
Option 2: play with physics values. You can spend a lot of time playing with those values. Increasing the linear drag on the player's rigidbody would help, as that dampens its movement. But you'll also have to repeatedly tweak your gravity, mass, and the force applied to the character when the player moves it until you find a good balance.
Option 3: use a collider for the walls that has a friction of zero, and walking surfaces get a collider with a positive friction. This is obviously more resource intensive, but that might not be a problem for you.