How can i change animation while sprinting?

My game like a lot of games has a shift to sprint script which does nothing except speed the player up when shift is held down and I was wondering how i could make it so that when i hold shift another running animation plays here is the current shift to sprint script I'm using: there is a regular script:

function onPlayerEntered(player)
	repeat wait () until player.Character ~= nil
	local s = script.SprintScript:clone()
	s.Parent = player.Character
	s.Disabled = false
	player.CharacterAdded:connect(function (char)
		local s = script.SprintScript:clone()
		s.Parent = char
		s.Disabled = false		
	end)
end

game.Players.PlayerAdded:connect(onPlayerEntered)

and inside of the regular script there is a local script:

local mouse = game.Players.LocalPlayer:GetMouse()
local running = false

function getTool()	
	for _, kid in ipairs(script.Parent:GetChildren()) do
		if kid.className == "Tool" then return kid end
	end
	return nil
end


mouse.KeyDown:connect(function (key) -- Run function
	key = string.lower(key)
	if string.byte(key) == 48 then
		running = true
		local keyConnection = mouse.KeyUp:connect(function (key)
			if string.byte(key) == 48 then
				running = false
			end
		end)
		for i = 1,5 do
			game.Workspace.CurrentCamera.FieldOfView = (70+(i*2))
			wait()
		end
		game.Players.LocalPlayer.Character.Humanoid.WalkSpeed = 24
		repeat wait () until running == false
		keyConnection:disconnect()
		game.Players.LocalPlayer.Character.Humanoid.WalkSpeed = 16
		for i = 1,5 do
			game.Workspace.CurrentCamera.FieldOfView = (80-(i*2))
			wait()
		end
	end
end)

Here's your script with a few changes:

local mouse = game.Players.LocalPlayer:GetMouse()
local running = false

function getTool()  
    for _, kid in ipairs(script.Parent:GetChildren()) do
        if kid.className == "Tool" then return kid end
    end
    return nil
end


mouse.KeyDown:connect(function (key) -- Run function
    local oldId = game.Players.LocalPlayer.Character.Animate.Run.RunAnim.AnimationId
    key = string.lower(key)
    if string.byte(key) == 48 then
        running = true
        local keyConnection = mouse.KeyUp:connect(function (key)
            if string.byte(key) == 48 then
                running = false
            end
        end)
        for i = 1,5 do
            game.Workspace.CurrentCamera.FieldOfView = (70+(i*2))
            wait()
        end
        game.Players.LocalPlayer.Character.Humanoid.WalkSpeed = 24
	game.Players.LocalPlayer.Character.Animate.Run.RunAnim.AnimationId = "" -- 						animation ID while running
        repeat wait () until running == false
        keyConnection:disconnect()
        game.Players.LocalPlayer.Character.Humanoid.WalkSpeed = 16
	game.Players.LocalPlayer.Character.Animate.Run.RunAnim.AnimationId = oldId
        for i = 1,5 do
            game.Workspace.CurrentCamera.FieldOfView = (80-(i*2))
            wait()
        end
    end
end)

Hope this helps!