Will i need to make any changes to my existing system for a Solar Thermal upgrade?

No- there are no required changes to your existing system. However, if you have a backflow preventer installed in your house then you will need an expansion tank in the dhw loop. Without this installed, the solar loop will be rasing the temperature of your existing tank and subesquently raise the pressure. Typically this pressure is absorbed by the line pressure from the municipal supply or well pressure but with a backflow preventer this cannot happen so you will need an expansion tank.