Are you adding a video card is that why the upgrade? Any way power supplies are all standard sizes just remove the 4 screws from the back and ann the plugs from the motherboard and drives. They can be longer but most dont vary to much. Now do all that in reverse LOL. It's not hard just make you you plug in both motherboard power connections and all the drives power.
Since your PSU conforms to the ATX12V PS/2 form factor:
Dimensions: 150mm W x 86mm H x 140mm D
or 5.9"W x 3.4"H x 5.5"D
Depth is the only spec allowed to vary. Higher capacity PSUs will protrude deeper into the computer case. You would need to check if there is sufficient space to handle this if you're upgrading to one of these higher power PSUs.
Make sure your new PSU has enough PCI Express supplementary power connectors if you're also planning on upgrading the graphics card.
The new PSU will most likely have several cables that weren't present on your OEM PSU and you will need to hide the ones you're not using, probably in an unused drive bay, so that it doesn't impede air flow within the computer case.