Fix typo in document

Author: KennyDizi

docs/docs/usage-guide/changing_a_model.md

@@ -212,4 +212,4 @@ To bypass chat templates and temperature controls, set `config.custom_reasoning_
 [config]
 reasoning_efffort= = "medium" # "low", "medium", "high"
 
-With the OpenAI models that support reasoning effort (eg: o3-mini), you can specify its reasoning effort via `config` section. The default value is `medium`, you change it to `high` or `low` based on usages.
+With the OpenAI models that support reasoning effort (eg: o3-mini), you can specify its reasoning effort via `config` section. The default value is `medium`. You can change it to `high` or `low` based on your usage.