peugeot zenith flat back tyre?

Hi. I sat on the back of my landlords zenith and as we turned a corner it went flat (no BANG/explosion). He did think that last night it might be somethhing wrong with it (already a bit low?).. anywey, I didn't have a pump here at the moment, to try at least to put enough to take it to a petrol station (far away). I can't! find a manual to remove the tyre either.. which seems to be a tad overkill if it is only to pump it up again.. ideas? we are short on money so do not want to take it to a garage just for a whopping fee, when it is something we should be able to do ourselves (well I at least).