How should I upgrade my PC to be able to handle video editing better? (Read Details)?

You have a good enough system to do video editing right now. But you're saying the playback is bad, not the editing part. Does playback of videos at any other time lag, for example while playing Youtube videos? You also didn't mention what type of videos that you're trying to edit. Are they standard 1080p videos, or 4K videos? How long are the videos? What type of encoding format is being applied (eg. Mpeg-2, H.264, Divx, etc.) Etc.

If they're large video files, let's say 1080p video that's over 10 minutes, or any 4K video, then it's likely that you're having trouble loading them in from the hard disk quickly enough. My suggestion would then be to buy an SSD, but also to keep your existing hard drive. With an SSD, you would be placing all of your programs and operating system files on the SSD, while placing data like your video files in the hard disk. The SSD will take a lot of load off of the hard disk, allowing it to dedicate its work to reading the video files.

On top of that, if you're doing a lot of 4K or long 1080p videos, then possibly going from 8GB to 16GB should help. But I'd say the SSD is more of a priority over the RAM.

And finally, most modern video cards these, including your 660Ti has built-in hardware acceleration for creating some specific formats of video encoding. Most likely it's the H.264 format that has hardware support. this makes a huge difference in speed for encoding these files. If you choose any other format such as Mpeg, or WMA, or DIVX, then you may not get the advantage that the video card provides for H.264. So it's in your best interest to always encode in H.264. Also make sure that your editing software has support for "hardware assisted acceleration" in its options.

I won't suggest doing anything with the processor, as I know that it is good enough, I've edited in lower hardware than that, and it's okay.

Video editing should have the fastest Intel i7 processor there is, 16 - 32 GB of RAM, a 512 GB or 1 TB SSD to write the files to, and so on. Unfortunately, I do not know if the video card matters or not. If it does, the best NVidia card that you can afford is in order. If you build a system like this, you will not have any video editing problems.

~Cindy! :)

You need a better graphics card. I recommend nvidia or amd. Before that tho try updating your video card driver