Recommendations for a dell optiplex 380 upgrade?

I recently purchased a dell optiplex 380 desktop for my little brother. It has a Pentium E5800 (3.20 GHz) core, 8 GB DDR3 RAM, 1 TB HDD, Intel integrated graphics, a 255 Watt power supply, and a Windows 10 operating system. I'm trying to upgrade the graphics and power. From what I've read, the GPU needs to be single slot, and low profile (which rules out high performance graphic cards). I'm trying to upgrade the system enough for my little brother to be able to surf the internet and play lower intensity games (like minecraft and roblox). Since returning the system isn't really an option, does anyone have any recommendations? Is it even possible to be able to play those games with this system?