Is it possible to upgrade to an SSD? Of course! But given your case and I have a feeling you single-partitioned your hard drive, a simple migration is going to be a pain in the ass.
In order to make this as painless as possible, you would need a 1TB SSD so you can do a simple clone over to it. But those things cost like $400 and since this is about storage, I'd cringe at the missed opportunity to get a smaller SSD and say a 4TB hard drive (which would still cost less!). The best option, in my opinion, is to get an SSD and reinstall your entire system on that. This solves two problems: migrating from a 1TB drive to a smaller SSD and your system bootup/shutdown. I have more reason to believe your system may just be rampant with stuff that you're not aware of (background tasks? Loading programs you don't need on startup?).
Also, don't worry about losing your program settings! As long as you don't touch your HDD while you set up everything on the SSD, and assuming you use the same exact user name on the new install, you can copy and paste the C:\Users\[username]\AppData folder on your HDD to your SSD and most of your program settings will remain intact. A little trick most people don't know about
(although I would recommend only shipping stuff piecemeal... most cleanup tools don't touch the AppData folder and it can get filled with crap you may not need or use).
As for what size... 250/256GB should be good enough. Install the OS and key, commonly used programs on it. Storing documents, music, videos, and pictures on a SSD is not worthwhile (because these are low bandwidth files which to you at 120MB/s and 500MB/s would open up instantly anyway) and in some cases may even make things worse if you're editing them often. Think of an SSD more of a WORM (Write Once, Read Many) drive than a traditional HDD. Other programs you use occasionally and... so far in my opinion many games, keep those on the hard drive.
Once you have everything setup and you're satisfied, start nuking the old stuff on the HDD. I would recommend a reformat, but you need a backup drive for that.
If you do want to migrate to an SSD without reinstalling, you would need to shrink your C:\ partition to the smallest it can get and get an SSD that can hold that + 1GB. The reason is... well migrating isn't as simple as cloning the hard drive partition. But once you're ready, you have to do the following:
- Go to Control Panel -> Administrative Tools -> Computer Configuration -> Storage -> Local Storage (I think... ). This should pull up the hard disk manager thingy.
- Add a 200MB partition on the SSD, format it as NTFS and give it a drive letter of S:\
- Right click on the partition and mark it as Active
- Clone the Windows partition on the HDD to the SSD (You have to use a cloning tool like EaseUS Partition Magic or something. You cannot just copy and paste).
- Open up command prompt as an Administrator
- Execute the following command
Bcdboot [Letter of Windows Partition on SSD]:\Windows /s S:. Bcdboot
- Reboot and attempt to boot from the SSD.