Recommendations to make my computer load and run faster?

This is my current build (It's really shitty, I know but it's all I have the money for): https://support.hp.com/si-en/document/c03359045.

Replace the graphics card with GeForce GTX 950.

I'm very new to building computers so please go easy on me lol. So my computer is able to run games fine thanks to the upgraded gpu but load times are crazy slow. I could be waiting at a fallout 4 load screen for over 2 minutes at a time, not to mention the 30 minutes it takes for my computer to turn on.

I'm here to ask on ways to improve the load times on my computer. I believe upgrading the HDD to a SDD would improve load times and upgrading the cpu would also help the computer run faster. The only problem is is that I don't really know what CPU I should buy and if it's even compatible with my motherboard.

Another option I was thinking of is to just buy a newer pre-built desktop online for a cheap price and then replace the GPU with the one that's currently in my computer. This is more of a last resort though because that would probably be more expensive then replacing parts.

Thanks for any help you guys can provide!