Dell optiplex 7010 sff (i5-3470) gpu upgrade

If you want a very basic GPU then the GT 640 will work and being a low profile card, it should also fit. But there are other options and this forum thread has more information.

As for the RAM, the most compatible RAM for a Dell system is from Crucial. That RAM can be found here. And if the cost is within your budget possibly a 2 x 8GB kit giving you a total of 16GB. If you pull the 2 x 2 modules that would leave the other 2 RAM slots open for further expansion.

Re: can I install other 2x2gb DDR3 PC3-10600U 240-Pin RAM stick in my PC

yes. unlike later model dell desktops that use faster ddr4 ram, in my experience the dell desktop pc that uses ddr3 memory are quite flexible with the brand of memory, as long as the memory speed is c/w Dell spec.  Pretty much any major name brand works with 7010, 790, 780 etc(all these models use ddr3).  there is no preference for a particular brand, so Samsung, Micron, Elpida, Kingston, Crucial etc. all work as long as the speed is correct.

For 7010 my experience is pc3-12800 and pc3-10600 both work.

Re: I just want install a more powerful gpu

I would recommend the Dell oem low profile gpu for 7010, 1 GB AMD HD7570, HD7470.

A-Tech is a good RAM brand I've use for years.  Lower cost than Crucial and has a lifetime warranty.  I'm currently using it with Hynix* in my 7010.  *To the best of my memory.