PSU fans are relatively easy to replace IF you show how to solder. The fan uses a non standard connector or it's soldered right to the PC board. Easiest thing to do is cut the wires leaving some length on them, splice the new fan's wires to the old wires, solder and use heat shrink tubing to insulate the splice.
As for mounting the fans are almost always standard fans.
BE AWARE that opening the PSU will violate the warranty.
Also be aware that if you damage anything in the PSU that you could damage your mobo or other equipment.
Also, don't leave the PSU plugged in while working on it or testing it. There's high voltage wall current in there - you can be injured or killed.
If it's under warranty you should RMA it.