NEW YORK--(BUSINESS WIRE)--Bolivia and Paraguay, two of the largest natural resource exporters in Fitch Ratings' 'BB' category, are well positioned to weather the ongoing downturn in commodity prices mainly due to relatively strong fiscal and external balance sheets, Fitch Ratings says. Rating upgrades of both these countries in 2015 were in contrast to the negative rating actions the other peer commodity exporters experienced. Fitch upgraded Bolivia to 'BB'/Stable in July 2015 and Paraguay to