Eh? You can change the team completely, for free, before the first game of the season - only use 'bench boost' if you are confident all 15 players will be playing (that's a one-off option per season), wild card is if you want to change a large number of players during the season, ie your team is shit and you need a total re-think, you get one wild card in each 'half' of the season. Free-hit is an option to change any number of players without penalty costs, but is only active for a single week, after which the team reverts to previous line-up, it's useful, say, on cup qtr-final weekend when a number of your team may be playing cup games whilst there are still league games in the schedule.
You can swap any players from your bench to your team without penalty each week, and change captain whenever - captain gets double points so is an important pick, something I consistently get wrong!