Fixed some grammatical errors

clean-up.md

@@ -13,9 +13,9 @@ In the lessons for each project, you may have created some of the following:
 * A custom vision project
 * A cognitive services resource
 
-Most of these resources will have no cost, either they are completely free, or you are using a free tier. For services that require a paid tier, you would have been using them at a level that is included in the free allowance, or will only cost a few cents.
+Most of these resources will have no cost - either they are completely free, or you are using a free tier. For services that require a paid tier, you would have been using them at a level that is included in the free allowance, or will only cost a few cents.
 
-Even with the relatively low costs, it's worth deleting these resources when you are finished. You can only have one IoT Hub using the free tier for example, so if you want to create another you will need to use a paid tier.
+Even with the relatively low costs, it's worth deleting these resources when you are done. You can only have one IoT Hub using the free tier for example, so if you want to create another you will need to use a paid tier.
 
 All your services were created inside Resource Groups, and this makes it easier to manage. You can delete the Resource Group, and all the services in that Resource Group will be deleted along with it.
 
@@ -35,4 +35,4 @@ Are you sure you want to perform this operation? (y/n):
 
 Enter `y` to confirm and delete the Resource Group.
 
-This will take a while to delete all the services.
+It will take a while to delete all the services.