I know its a long time since this question was posted but I had the same issue and have just fixed it. Remove the toilet seat by pushing in each of the two release buttons on the hinges, then lift. Where the hinges located are two circlular receivers, both have a metal cap that can be removed using a small flat head screwdriver or similar. This reveals a large cross-head bolt head on each which you can tighten. I suggest nipping them up not overtightening just in case you damage the bowl. At least once you know where they are you can re-tighten another day! Then reassemble (remembering to put the caps back on first)... I hope this helps someone - I spent ages looking for the answer on the internet only to find it all out myself. Good luck...

Hi, i have the same issue as my seat is loose. i have removed the seat which leaves a metal plate with two round pins sticking uip. there is no access to the back of the toilet or underside where the bolts would be as its a back to the wall toilet. any ideas?