Sliding Patio doors come off runner...

Raksha

After a temp fix earlier this year, the sliding patio doors which divide our living room from the porch have come off their runners due to the 'stopper' block of wood coming off and excess force being used when opening them (two teenage sons and an OH who always know better)

OH has a bad back, and can't do any heavy lifting (and I'm not great either), 17 year old son is a BTEC engineering student (but very little practical experience)

Can anyone give us a 'dummies guide' to fixing them. I believe last time the runners were lowered onto the rails when the doors were replaced, but I don't have the foggiest idea how this was done, and it's now proving hard to remove the door at all.....