To change between coordinate systems we will be using a program called VDatum. You can find the download here.
After downloading unzip and open the folder. Open the folder called vdatum then scroll down and open the file called vdatum.jar.
You will then select the coordinate system and unit system of the coordinate you are converting from underneath the ‘Source’ section.
Then you will select the options shown below for the ‘target’ section.
Lastly enter your points into the point conversion tab and then click convert!
After converting your base coordinate follow through to Selecting the Base Coordinate.