Almost the worst possible thing to do is upgrade Memory along with a new HDD.
You do not NEED more RAM.
When I added an extra 4 GB of RAM to the existing 4 GB ( 2 new chips added to the existing pair ) it failed to boot.
Removed the new chips and it booted.
Added one chip and it booted.
Several combinations of any 3 chips gave me 6 GB and boot-ability.
Last desperate attempt and all 4 chips were each in the only socket that gave me 8 GB that would boot.
For me the optimum procedure is to use Macrium Reflect (or alternatives that I have no real experience of),
and use it to save Partition image backups to an external device,
and use it to create a WinPE Boot Recovery CD that will restore its backups to any HDD
( including the new empty HDD which has no Windows ).
Please note that I have 6 different USB2 Flash drives from different suppliers and different makes,
Most of them read back at between 15 and 25 MB/s.
All of the are restricted to writing at about 25% of the Read speed
( the fastest writes at 7.24 MB/Sec, the slowest writes at 3.36 MB/Sec )
My partition C:\ size is 55 GB, of which Used Space is only 11 GB, and a backup is about 6.5 GB,
which would probably take 2000 Seconds if I were to save it to a USB2 Flash Drive.
2000 Seconds is nothing compared to using Windows Installation Disks and installing all the patches,
but once you start using image backups in anticipation of future disasters you will appreciate using an external USB2 HDD at 20+ MB/Sec
(an USB3 HDD is even better.)
After you have a fully functional system you will then be in a better position to know what to UNDO if extra RAM goes wrong for you,
and you can focus on making sure that you have not damaged the RAM socket contacts and can try shuffling your chips around.