I don't believe you have to import again just go into the Texture drop-down in the Inspector and change it from "Inherit" to any one that says "Nearest".
It should be in" Canvas Item > Texture > Filter". Set it to Nearest. Also, you can set it to "Nearest" on the parent node and leave the children nodes as "Inherit" and they will use the crisp pixel look.
In inspector look in Canvas Item -> Texture -> Filter
Hope this helps.