Can someone teach you how to take a character skin such as Tali from Mass Effect and put it into another game such as Dead Space 2 and stuff similar to that

As far as I am aware, there are no conversion utilities for any of the Mass Effect or Dead Space series, but there are many simple ways to extract models and textures from just about any game (3D Ripper, X-Ripper, etc). Converting them to another game is more difficult to do since they require packaging in the game engine's format. However, there are ways to temporarily replace textures locally without changing any game specific files using an application called TexMod.