Unfortunatly later model Renaults did away with the dipstick in favour of the electronic sensors, Mine has both dipstick and sensor.
With the Clio (and it should be similar on the Scenic) you need to locate the following:
1. Fill tube ~ normally at the front of the box and will probably have a cap / bung in it.
2. Drain plug ~ should be under the gearbox sump but exact locations vary, mine was not where the Haynes stated.
3. At the front of the box there should be a plug. This is where a plug in ATF fluid dignostic is used by dealers to tell if you have enough fluid.
If you have all 3 located (and correct tools and replacement ATF) then the following is a rough guide.
Remove bung from (1) above, under car put an old bowl under the sump and remove sump plug, drain
and cycle the gear stick through the range a few times.
stopped coming out, refit he sump plug and remove the plug in (3) above (level plug) fill with ATF through the top plug (1) until ATF dribbles from the level plug. Refit all plugs, start engine and again slowly cycle through all gears (to fill torque converter) a couple of times. Leave to settle and remove level plug and bung and add ATF as required, refit all and test drive.
I did this on mine with great success (the only difference being the use of the dipstick for level checking. The procedure is in the Haynes manuals for the early Clios but I am not sure about the Scenics. Also note that there is a disclaimer that levels should be checked using Renault Diagnostic equipment (before giving the above instructions)
If you wish to go ahead I personally dont think it will hurt ( I would do it myself) but obviously the choice and responsibilty is yours.
Oh yeah the ATF should be red in colour. If it semlls burnt and is black / brown and particulate then it was due a change.