Are you sure it's not my cat I lost in the 70's?

Jolanta, I have been knitting and spinning my whole life (hence my screen name) First of all, decide if this is wool or acrylic yarn. If it is acrylic, no fuss at all. Just prepare a nice hot bath using shampoo and wash the skeins as it. Rinse well and let dry. You could put the skeins in a pillowcase and dry them ion the dryer. The pillowcase will prevent the yarn from tangling.
If it is wool, you'll need to proceed more carefully. Again, you'll need a warm bath using shampoos, Let the wool sit in the bath without much agitation. After a while, lift it out carefully. Dump the wash water and draw a rinse bath ( repeat this several times, if very soapy. The trick to washing wool (sheep, Alpaca, llama,) is to treat it like a baby- carefully. When sufficiently rinsed, let it drain, then roll it in a bath towel and let it dry.
How can you tell whether it is acrylic or wool? Use the burn test. snip off a length and light it with a match. The acrylic will burn into a black ball ( it is made from oil after all) The wool will burn into a long gey black snake of fiber.
You can probably sell your stash. Some knitters prefer acrylic, other wool.
Facebook now has "markets" for unwanted stuff.
Much luck! Let me know what you have. I may be interested.