you welcome
1) very easy ,lay down the case and in the back unscrew the 2 screws thats holding the door and open it, disconnect the main 20 pin plug and the 4pin from the mobo & disconnect the power plug from the graphic card & hds/opticals , in the upper back unscrew the 4 screws thats holding the psu , use both hands to hold it from bottom & top move it bit backward then up, thats about it on how to take it out the how to put it in is obvious
2) it will fit for sure , its standard atx size just like your current
3) as i alredy said its the
ampers that truly matters not the watts , it will be more then enough
4) they will come handy if youll upgrade , just use a standard power plug for it
5) the voltages depends on the load placed by the various parts & how the psu handles it depending on its amper ratings , your psu is stressed nearly to the max , and its very cheap and underpowerd one too.. , you might be able to make it bit better by underclocking the processor & disconnecting power plugs from unnessary devices