Both reformers and revolutionaries want change. However, the scale of the changes that they want is very different. Reformers want much less in the way of change than revolutionaries do. Since you tagged this with “progressive era,” let us discuss this difference with reference to that time period.
In the Progressive Era, the Progressives were definitely reformers and not revolutionaries. They felt that there were many things wrong with the political system and with society in the United States. However, the changes that they proposed were relatively modest. For example, the Progressives believed that big businesses were abusing their workers. Their proposals to remedy this were fairly modest. They simply wanted the government to impose regulations that would require better treatment.
By contrast, there were some revolutionaries at this time. The socialists were an example of these revolutionaries. The socialists were not content to ask for small changes like government regulation. To them, the solution to the abuses of big business was to take away the businesses’ right to exist. They would have liked to have government control of major industries. This is a much more radical proposal. This shows the difference between the reformers (Progressives) and the revolutionaries (socialists).