I purchased Day Lillies about 8 years ago to put around my mailbox pole they grew great and new ones helped fill in the area nicely. In the last couple years I have not seen the plants spreading. They are healthy and producing beautiful flowers. Do I need to transplants some of them? I would like to put them in my other gardens I have not found these anywhere I can only find tall ones these are perfect for a border. If I should or can how and when is the best time to do this.

Your Day Lilies may have become root-bound. That is when blooming suffers.
8 Years is wayyyy to long! Usually, DL's need to be divided every 3 years.

Dig up all of them--hose the clump clean and then look to see where you can divide them.
Usually--every clump of leaves also has it's own roots. SO! If you cam manage to pull
all the leaf-clumps apart--you should have nice sections to re-plant. share, give away etc...
If they are all to big a solid mass of roots--get a nice sharp kitchen knife and cut them apart.
YES! You can do this!!!

If you do this--and re-plant your divisions--you will not see blooms the next year.
But--the year after that--you should have a nice, blooming, fresh bunch of DL's.

Gita