Friend needs advice on upgrading his prebuilt PC, help is very welcome.

He was gifted a prebuilt that is running horribly and severely handicapping his gaming experience, I think its running worse than the specs would otherwise indicate but I need help on what to upgrade/what can be upgraded.

Specs according to Speccy:

Operating System Windows 10 Pro 64-bit

CPU Intel Core i5 4440 @ 3.10GHz 52 °C Haswell 22nm Technology

RAM 12.0GB Dual-Channel DDR3 @ 798MHz (11-11-11-28)

Motherboard Dell Inc. 088DT1 (CPU 1) 28 °C

Graphics ASUS VK278 (1920x1080@60Hz) Intel HD Graphics 4600 (Dell)

Storage 931GB TOSHIBA DT01ACA100 (SATA) 37 °C 3GB General UDisk USB Device (USB)

Optical Drives TSSTcorp DVD+-RW SH-216DB

Audio Realtek High Definition Audio

Thanks for any help in advance! You guys are usually pretty awesome at helping me and my various computer needs :)

EDIT: Model/Case is an Inspiron 3847