According to the policies set forth by UNM, a student has three key dates before which they can drop a course. The first is to drop “With 100% Refund and Without Grade”, the second is to drop “Without Dean’s Permission” and the final is to drop “With Dean’s Permission”. As these dates vary from semester to semester, you can view them at the UNM Registrar's Page (Deadline Dates on the left side).
The first two drop types, "With 100% Refund and Without Grade" and "Without Dean's Permission," are done through LoboWeb - see the instructions UNM has provided: https://unm.custhelp.com/app/answers/detail/a_id/5265/kw/drop/related/1
The third drop type, "With Dean's Permission," requires a form: http://www.unm.edu/~unmreg/images/Forms/EnrlAuth-LateDrop.pdf . For more information, see the UNM instructions: https://unm.custhelp.com/app/answers/detail/a_id/5691