I see so many questions with spelling and punctuation errors and I sometimes correct them. Is that right or it is better if I ask the one who has written the question/answer to edit it and improve it.
If you can improve a post, it is best to simply edit it yourself. Users with lower reputation can make suggested edits that can be approved later through the review queue. This is at heart of what wiki editing is about in Stack Exchange.
Trying to orchestrate this through comments only leaves a mess behind to clean up later.