Michael Jackson says Shrewsbury will rebuild after their 4-2 loss to Peterborough condemned them to League Two football next season.
Shrewsbury needed to win to keep alive their hopes of an unlikely great escape.
But Posh proved too strong going forward and could even afford the luxury of a missed penalty, when top scorer Britt Assombalonga's spot-kick was brilliantly saved by Chris Weale.
Conor Washington netted twice for the rampant visitors while Lloyd Isgrove and substitute Josh McQuoid were also on target as Shrewsbury replied through Jon Taylor and Tom Bradshaw.
He added: "This club's got an opportunity now and we've got to move forward very quickly. We've got to start building for the future and we can't let things like that happen again, what's happened this season.
"It's been difficult and it's been hard for everyone involved, and that's supporters as well who I feel sorry for.
"We've got a responsibility now to make sure we develop this club from top to bottom as that's what needs to be done. We've got to look towards that now and that's massive.
"We know what's gone wrong, we know all that already, so we've got to look to the future as soon as we can and get over this disappointment quickly."