But be wary of the fact that any app purchases you made will be tied to the original Microsoft account. If you purchased a lot of apps, you will not have access to them again if you sign into your phone with a different Microsoft account after the hard reset.
If someone else set this up and you haven't used it for any app purchases or the like it should be a simple matter of going to settings>email>long press on this account and select delete. As long as you don't add it again, it should be gone from your phone.
If you have used it for app purchases or downloads, then a hard reset would be necessary.