Question

President Washington believed that the best way to change to constitution is through

Answer 1

Answer;
President Washington believed in the amendment process laid out in the constitution that that was the best way to change the US constitution and that way followed the legal norms for implementing changes and ensuring that it was done successfully.

Explanation; 
He admitted to imperfections in the new charter but trusted the amendment process to refine it. For him the beauty of the constitution was that it charted a path for its own evolution. He believed it was very brevity and generality; which means it would be a constantly changing document, susceptible to shifting interpretations. 

Answer 2

I would say he believed in the amendment process laid out in the constitution that that was the best way to change the US constitution and that way followed the legal norms for implementing changes and ensuring that it was done successfully.