Things to consider:
1. CPU (check the CPU compatibility list of the motherboard)
If the fastest CPU supported by the motherboard is only a small improvement, a new motherboard might be needed, and that maybe supports faster RAM also. But that surely increases the costs to CPU + motherboard + maybe RAM
2. replace HDD by SSD or add SSD for the OS and programs
I have a custom made PC for 4 years, but I have very little involvement with its building or choosing the parts. Although the old guy has served me well, I believe it is time to upgrade it. The problem is that the budget is limited.
Intel(R) Core(TM) i3-3220 CPU @ 3.30GHz
8.0 GB DDR3
Gigabyte Technology Co. Ltd. B75M-D3H
AMD Radeon HD7700 Series 1Ghz 1GB GDDR5
Which of these should I upgrade first? I game very little (mostly LoL and HS) so I prefer better overall performance, rather than gaming performance. Moreover, I use photo and video editing programs (Photoshop, Premier, etc).
Thank you for taking the time to read this! Any help wil be highly appreciated