I've just ordered a Crucial M550 128GB 2.5inch SATAIII SSD to fit in my Acer V3-771. I have a spare drive bay so will fit it in there alongside my current hdd, and re install my os on to the ssd. I have read in a couple of places that the serial number will be embedded in the bios and i wont need to put it in again. Is this correct and will i need the original recovery discs to do this(I've no idea where i put it)?
Ideally find your Recovery disks as I'm uncertain if any installation disk will work on a pre-installed Windows 8 PC. If you don't find them, you can create your own backup. (Won't work on a PC upgraded to 8.1 from 8) Backup for 8.1 Laptop with Recovery Partition
Best advice would be to create your Backup on a separate Drive, that way you have a reliable backup should your HDD fail. Check your C drive to see how much space you've used to install Windows, (Rt click 'C' and choose Properties) Ideally use a Flash drive 32 Gb USB3 should suffice, on Ebay around £10/$16 Simply plug in your Drive and type 'Recovery' at your Start Screen and 'Create Recovery Drive' (From Settings, W8).Tick the Option to copy Recovery Partition.
To recover, boot from the Recovery drive and use Troubleshoot/Advanced Options to get to Reset your PC, which will allow you to restore Windows to new HDD,SSD or replace a corrupt OS.
In your case I would swap the HDD for the SSD and connect the HDD in the 2nd drive bay after you've finished.