Need help installing ssd

(Idk which subreddit to post this to so I'm posting it here for now )
So I use a Lenovo IdeaPad s145 laptop and it needs a serious upgrade. I'm thinking of installing a 4gb ram stick and 250/512 gb SSD
I need help with SSD installation
How do I install one ?
(ik the physical processe ofcourse there are tons of YouTube videos)
My question is with the software part like how can I install it without losing Any data (the data is super duper important) and backing it up in an external drive is not possible cause it's about 500 gb in size and I don't have one either and I don't wanna remove my hdd I wanna use it as a storage backup (it's size is 1tb and I wanna boot the OS in SSD)
Can someone please explain it step by step (only the software part) and if not please provide me with useful links for this process
Help will be much appreciated 👍
Well I have done this many times before. I purchased a external drive case to clone the drive I replaced. Now you may find a kit that come with the USB case and the imaging software at a place like Tiger Direct. No the software you need is imaging software and I have always used Acronis True Image. What the software is boots up into the software and it uses a source drive and the drive you want to copy to the target. You run the software and it duplicate the source. You replace the source with the target. It's best if you have multiple drive you remove the second drive and force the PC to boot with the copied drive. Then that will make sure that drive will be the boot drive. Then you can put the 2nd drive back in and the system will not the copied drive is the boot drive.