Do you mean AGA? If you mean AGA you have to get an A1200 or A4000. If you're looking at games website ECS also means OCS, so no upgrade needed. ECS/OCS is an abreviation for non-AGA Amiga (old chipset, enhanced chipset).
On the motherboard Agnus basically came in 3 types: 512k for Amiga 500, 1MB for Amiga 2000 making OCS. 2MB for Amiga 3000. Chip memory is similar to graphics memory on a PC.
Super Denise, plug in replacement for Denise added some screen modes (still only max 4,096 colors) and one command was sped up.