If your friends revolver doesn't have the top strap over the cylinder it is a reproduction of a Colt.
If it has a closed frame with a top strap over the cylinder it is either a Remington like yours, a Whitney or (if he is very lucky) a Rogers & Spencer.
Most likely it will be the open top Colt.
(I am excluding the Confederate copies because they were basically rather poor copies of the Colt or Whitney.)
You really should look around the forum. There are literately hundreds of posts about cleaning these guns but briefly, soap and water along with a cleaning jag and cotton patches are all that is needed. Black powder fouling dissolves in water and any ball or bullet lube that might have been used will be taken care of by the soap.
It is not necessary to completely take either pistol apart. Removing the cylinder and the nipples and cleaning them, the barrel and the exposed areas of the frame is good enough.
To remove the cylinder from a Remington place the hammer at half cock.
Lower the loading lever, grab the two ears that form the "T" head on the cylinder pin, pull it towards the muzzle.
When the cylinder pin has moved forward, the cylinder will become loose and drop out of the right side of the frame.
When replacing the cylinder, make sure the cylinder pin is forward, insert the cylinder into the frame, rotating it in the same direction it normally rotates as you do.
This rotating of the cylinder will push the cylinder hand that normally rotates the cylinder back into the receiver. With the hand pushed back, the cylinder will move freely into place.
To take the Colt apart for cleaning, first drive the barrel wedge towards the left hand side of the gun. Use a piece of wood or plastic between the end of the wedge and whatever your using to tap it with.
This wedge won't come all of the way out of the barrel. It is retained by the small screw head on the left side of the barrel.
It only has to be removed far enough to disengage with the cylinder pin that the cylinder revolves on.
With the wedge partially removed, place the hammer at half cock and rotate the cylinder until the loading ram will hit between two chambers.
Then, lower the loading lever driving the ram back into the face of the cylinder.
Pushing it down a bit more will "jack" the barrel off of the cylinder pin.
One the barrel is removed, the cylinder will slide off of the cylinder pin and everything is ready for cleaning.
When reassembling the Colt remember, that barrel wedge only has to be driven far enough to secure the barrel to the frame.
The right end of the wedge does not have to be fully protruding from the right side of the barrel. If the wedge is driven in too far it can lock up the cylinder.
Have fun.
