There is no one perfect solution to upgrading your PC. I have Lenovo Yoga Pro 2 that runs on 256 GB SSD, 8 GB RAM and i7 Intel and I have been using it for 3 years and it runs smoothly. The only problems I ran into were issues with its operating system, Windows. I had to refresh its OS a couple times and I even had to reinstall the fresh OS on it once.

Honestly, I would suggest you to upgrade your HDD to SSD and maybe install a reliable Linux distro on yours. Linux runs much smoother than Windows in some cases. Upgrading your RAM is a good move if you can be able to remove it manually. Some manufacturers soldered RAM on the motherboard, which I cannot upgrade mine at all.