That's strange. It automatically is set to greaters every time I download it.
Open the big black pally power menu box, command is something like /pp menu or something, that is, if you don't already have it open from right clicking the red/green movable dot. I didn't have to adjust anything to set greaters, just left click under the class icon in the black space and bam, greater blessing. To set normal blessings you have to do alot more work and actually right click a persons name, select which pally is buffing, then select the blessing... it shouldn't work any other way. Make sure you have the latest version.