There are only a few ways to get rid of days on your schedule at SWA. One is to give them away to another pilot. That's pretty difficult to do as not many trips get picked up in giveaway and most that do are one or two day trips. I was lucky this month and had a 3 day trip given away.
Another way is due to overlap/conflict resolution. This is dicey but I usually try to do it every month. It is a product of line bidding.
The other way is to ELITT (trade with the company). If another pilot from your base and seat trades up in ELITT then you can use that "net zero" to shed days. This is hit or miss, but I generally drop one or two days a month using this method. With ELITT you can also trade any of your line trips for other line trips that the company has in open flying greater than 4 days out. Most of these trips are weekend trips, although if you are diligent you can trade into weekday trips.
SWA makes it really easy to pick up extra flying, but much more difficult to get rid of the flying you have.