Peugeot 206 2007 1.6 Petrol Automatic 2 issues!

Hi all,

My Mum has the car named above and over the past few weeks two problems have come to light.nThose being as follows:
- "Automatic gearbox fault". I have been in the car only once or twice whilst thus has occured and ut seems to knock/jolt the car somewhat when this happens? I'm have seen a few threads in hear but as I'm not mechanically educated all the jargon gets confusing. When driving last night on the motorway this occured and when driving at speeds above 50/60+ mph I noticed the car seemed to be high up the rev range (above 3000rpm) which made me think that the car isn't selecting 5th gear. When we stopped after the drive I moved the selector over to the manual setting and pushed forward and confirmed my suspicions... The car will not go into 5th. From having a read this morning is this to do with the gearbox oil? If so how complicated is it to top up as this has never been topped up from new although the car has only done 31,000 miles from new? If this is the case could so,ebody please give referance to a step by step video on how to do this please? It would be very much appreciated.
- Water/greasy puddle in the passenger footwell. I have also read around this issue and two keep on popping up when reading this issue. First being the bulkhead may be clogged up from leaves and other debris. As I said before I have no mechanical knowledge really so have been looking for step by step videos on how to clear this but this is proving difficult to find also. However if this was the case am I right in believing that the wet footwells would be water rather than a greasy liquid? My elder brother has a look last week at this and tasted the liquid and said it tasted somewhat of coolant? When reading around this issue there are some suggestions that this is a heater matrix issue? If so would this be too complecated for someone like me to sort?
If anyone could help out it would be very much appreciated. It is a shame as I lost my father just over a year ago who was a mechanic for 40 odd years and would have had this issue rectified if only he was still with us. I have most tools any other mechanic would have I believe so wouldn't mind having a go. I just don't want to make the car any worse by me taking on a job too big.

Hope to hear back as soon as possible.

Many thanks