To make a road level to walk on (so does not slope to one side), stand on the higher of the two sides and examine the tile border that crosses the road to the lower side. You will need to do some combination of [[digging]] the higher side and dropping dirt on the lower side to bring this to "this slope is level".
In normal grassy areas, it may be possible to simply choose '[[flattening|flatten]]' on each tile as you walk along the road, but this often does not work because of rock, uneven numbers of dirt, lack of dirt in your inventory or low digging skill. A player with a higher [[digging]] skill may also flatten paved tiles of any type. The dig & dump method however will always work, unless there is a fence preventing dirt from being dropped.