I'd write it like this: "There is no longer any need to carry many thick books, nor spend too much time looking up words in a dictionary."

There are many ways you can make this sentence make more sense. I'll give a few of them. These are if you are expressing something about yourself: "I don't have to carry such thick books anymore and I don't have to spend too much time looking up words in the dictionary." "I'm so glade I don't have to carry those heavy books anymore so now I don't have to spend so much time looking up words in a dictionary." "I no longer have to carry such heavy books, therefore I do not have to spend so much time looking words up in the dictionary." That last two sentences express "cause and effect." Something does or does not happen THEREFORE it effects this other thing. You can also use "so" instead of "therefore" when talking. I hope this helps!