I have a 2007 2.4 gh iMac can I upgrade the logic board or what can be done

The memory can be upgraded to a max for 6GB (2GB in one slot and 4GB in the other). You can replace the stock mechanical hard drive with a solid state drive. Since SSDs are very fast they compensate somewhat for the lack of real memory the 2007 has. I performed this upgrade (it isn’t a quick easy upgrade, more of a moderate upgrade) and independent Mac dealers will do it. The Apple store will not.

Unlike the Windows world, logic board upgrades aren’t really feasible for iMacs.