MSI AMD Radeon R7 240 2GB DDR3 is compatible with the Lenovo Thinkcentre M58P 7484?

The MSI AMD Radeon R7 240 2GB DDR3 is compatible with the Lenovo Thinkcentre M58P 7484? - 1

Added (1). I know the problem with the psu of 280 ws, but if i change the psu, it will work?

Yes you can replace your ATI Radeon HD3470 256M PCIe with an MSI

Assuming you have a standard spec model.

You'll need to buy a 500w PSU

The Motherboard has a PCI express slot so it will accept the card - in general any motherboard manufactured in the last 6 years is compatible with any graphics card manufactured in the last 6 years. Of more importance is
a) Whether the card will fit in the case - some modern cards are dual slot and occupy a fair length and width
b) Whether the power supply will be sufficient and has enough connectors (some high end cards require 2 PCI-e power connectors)

Check the power requirements of the card and then check your PSU power output.
HTH
David