You can take a look at M2V-TVM | Motherboards | ASUS Global to find more information about your motherboard. VIA K8M890 is the very last VIA Chipset integrating the GPU for AMD platform. In theory, this chipset could support AMD FX processors, but before AM2+ processors released. VIA announce the exit of chipset market, and abandon further support for both AMD and Intel platforms. So there is no motherboard manufacturers enable it to support AM2+ and later processors. You can take a look at https://www.asus.com/Motherboards/M2VTVM/HelpDesk_CPU/ , pick up one of them you think is better, and update your system without problems.
The ASUS web site for that board list all of the compatible CPU's that you can use.
And, cpu-world.com can be used to compare CPU specifications so you can fine one you like.
Those are the CPUs that motherboard supports, which you can use assuming your BIOS is updated and your cooler can handle it. All of those processors are long since discontinued, as is Socket AM2, so your choices are limited to the used market.