Dim headlights are normally caused by their electrical connections being corroded or dirty. Unplug them and wire brush the contacts then reconnect them. Also disconnect, wire brush, and clean the black ground wire connecting each head light to the tub.
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Electrical contact cleaner can be used in conjunction with what Jerry said above. I've found that it helps to get the crud out. Also before reconnecting the connectors to the lights. put some dielectric grease on the contacts to help prevent future corrosion.
Backseat removal depends on which TJ you have. on my 01, I have to flip the seat in the up position. On each side where the bar inserts into the holding brackets, there are pins that insert on the bar to keep it from moving. If you pull those pins off, the seat should slide from side to side which allows you to remove the back seat.
Since you didn't say what year Wrangler you have, I'll add to what PTaylor said. On my '06, fold the rear set forward, push down on the bar that runs along the bottom, and pull the seat out.
Regarding headlights, if cleaning the connections doesn't work for you, it is very easy to replace the entire headlight. The stock lamps are sealed beam, so they don't have replaceable bulbs. Three torx screws hold the bezel, then three more hold the headlight on with a ring. If you want to upgrade to halogens, several companies make very nice headlamp replacements. I like my KC H4 Conversions. Others prefer Hella's.
Delta has a set of headlights that have the "white/blue" look H4 Xenon bulb for around $70 and trust me they are much brighter than stock! I had a problem fitting them but a bead of silicone fixed that right up.