its very easy to do
1) lay down the case and open it
2) disconnect all the psu cables from the board/devices
3) unscrew the 4 screws holding the psu and take it out
4) put in the new psu & its screws
5) connect all the cables to the board/devices (and do not forget the 4pin connector)
6) close the case, and power up (before you do make sure the on/off switch at the back of the psu is set to on,but it should be on by default)
the only way the psu will get fried after installing is if youll move its 115/230 voltage switch in the back (its a small red colored switch , its country specific. it should alredy come set as it should do not change it, some psus dont have that switch and have automatic voltage detection instead but most of em do have it)