Utah Code § 15-4-4

Subject to the provisions of Section 15-4-3, the obligee's release or discharge of one or more of several obligors, or of one or more of joint or of joint and several obligors, does not discharge co-obligors against whom the obligee in writing and as part of the same transaction as the release or discharge expressly reserves his rights; and in the absence of such a reservation of rights shall discharge co-obligors only to the extent provided in Section 15-4-5.