You may not be able to get there from here by changing chain rings. The bolt circle on a road triple crankset will not accept chain rings much smaller than the 30 you have now. (the bolt holes would be in the teeth).
You are probably looking at a touring crankset of about a 26/36/48 ring size to get what you want. Your road derailleur will still work ok with this crank. You can look at the Shimano LX series of cranks to see what this looks like although several other manufacturers also make such a crank.
To install such a crankset on a road frame will require you to know what your doing with regard to bottom bracket length.