Approving your scheduled posts can be done via the Dashboard. Here, within the queue, you will see all of your scheduled posts.
You will see in the bottom right of each post within your queue that it will either say
'Awaiting approval' - these posts are waiting to be approved before they will post, or
'Approved' - these posts have already been approved and will automatically post at the selected date and time.
To approve a post, simply click on the post within your queue, this will bring up the post preview in the right hand column, where you will have the option to change, edit or approve your posts.
If you are happy to keep the post as it is, just click approve, if you like the post but would like to review and make some tweaks, click the edit post button. If you don't like that post and would like to swap it for a different post within that category, click the change post button, this will bring up a library of the posts within that category for you to select from.
You can still edit approved posts or cancel them, simply click on the post in your queue and it will bring up these options in the right column.
If you cancel a post from your schedule here, it does not remove it from your schedule, but will simply revert to awaiting approval. If you don't want a post to go out on that date and time simply leave at awaiting approval and nothing will post. To delete from your schedule you will need to delete the recurrence within the recurring posts tab, more details can be found on that here.