what is a good upgrade from a intel d 326

For gx620, there is limitation for upgrading, because RAM is only up to 4GB DDR2, CPU is only Intel® Pentium® D, the GPU is only single slot because the space, if you get the new GPU you may need the new PSU too. So the best upgrading is to buy the whole new PC if you use the PC for games, if the PC is not for games then you just use it until it can't be used anymore.