If you have not yet filed it, yes, you can change it. Just open it and make whatever corrections are necessary.
Submitting the return for filing is just like dropping it into a mailbox - you can not get it back, cancel it, or change it.
Once you submit and find that you need to make a change, you will have to wait until the IRS either accepts or rejects the return. If the return is rejected by the IRS, then you can make the necessary changes and resubmit it. If the return is accepted, then the only way to change it is to prepare an amended return and file it by mail.