It is not easy to use miles to upgrade. It's not like you take your economy ticket and give them X miles and get upgraded. Policies vary by carrier, but sometimes you have to be in a certain fare class, which will usually not be the cheapest. Often there is a (significant) cash co-payment. You can get put on a waiting list. It has to book into certain fare buckets.

I'm not trying to rain on your parade. I can certainly understand wanting to get into J.