Manchurian :
I am also fairly new to installing hardware. Is a psu pretty easy to install?
You've got a new enough unit that the PSU I linked should work fine.
Basically you want one that has more capacity than your minimum requirement which you stated as 450W.
I'd go no lower than 550W and would even consider a 600W if the price was right.
Changing the PSU is not that difficult however you do have to be very careful and take your time.
Make sure you are plugging the proper connector into the proper place but before you do anything make sure you ground your bare hands/arm to the side of the metal case as you can damage sensitive components by electrostatic discharge and you don't want to do that.
The various plugs orient into their sockets a certain way and they all lock into place so if you look at them very carefully you can tell what goes where.
First you naturally have to disconnect all the plugs from the motherboard and drives in your PC just remember not to force anything. There's a tab on all of them that connect to the motherboard that you must squeeze in order to release the plug.
Once you've got them all disconnected there are four phillips head screws on the back of the case that hold the PSU in position.
Since I have no idea of the space in your case I will caution you that at times things are tight and I have actually had instances where I had to remove the motherboard or heatsink to get enough space to move the PSU in and out.
Large power supplies and/or large heatsinks will create such a scenario in a mid tower case.
Hopefully that's not the case as it makes for a much harder task.