First of all, go to Asgore's house in 'new home'.

Then go to the basement and follow the path until you see a crossroad that leads to some flowers.

Then get the key (I already have it, oops).

For the next step, you need to go to Sans' house in Snowdin town.

Then go behind it and interact with the house to go into the basement.

In the end, you'll see a strange covered machine on the right side of the basement. Interact with it and you're in Hometown!!

There's also an alterante way to go to hometown (you just need to do the first 3 steps before this by the way)

First of all you need to have dark world unlocked if you played in it in previous versions

For final, when you spawn at first the start of dark world, go down and you're in hometown :D

(Credits to @Zeen13 for this one)

Hope this helps!
-Elasmo-