At least in Chile, upgrades (via coupons or LATAMPASS kilometers) are only made available to elite members of the program. I've never been able to use my AA miles to upgrade, only to book full awards. There may be different rules for LATAMPASS in Peru, though. Check the Peru site of lan.com.

Unfortunately, the only option I'm aware of is to pay for the difference between Y and J. Your OWE status might help in an OP-UP situation, but don't count on it.