Having a 1tb drive already you will likely have a computer than supports this drive.
The relative ease of replacement has many factors, however once determined that you personally can get into the laptop to replace the drive, the migration of the operating system is typically done by purchasing a USB to SATA cable, where you will plug the new drive into the cable and into your USB slot, then with the drive cloning software you purchased you will clone the internal drive to the external USB connected drive (doing this before you replace the physical drive will alleviate any headaches with replacing first and then finding out something is incompatible..
Once you have cloned the internal drive to the external drive, open up the laptop and replace the old with the new drive, close up and start your computer.
As to the effect of the replacement... If your current drive is a standard 'spindle' drive type (non-SSD) then the significantly increased SSD read/write speeds will definitely make your computer feel faster!
Maxing out your computers memory will also provide a benefit.