The motherboard included on this computer is MSI Kaili2. It supports graphics cards with PCIe 2.0 and PCIe 3.0. The graphics card port is PCIe 2.1, so it is possible to add this card to the board.
Now, the current power supply provides with 460W. AMD recommends to use a power supply of 500 Watt or greater power supply with two 75W 6-pin PCI Express® power connectors.
AMD Radeon™ HD 6870 Graphics
It is necessary to verify with your desktop manufacturer if it is possible to replace the power supply.