The cryptocurrency transaction file I downloaded from coinbase contains transactions from 2018 & 2019. Do I need to include 2018 transactions while filing for 2019 taxes?

No ... 2018 transactions belong on the 2018 tax return ... they must be removed. 

Even if I carried over currency from 2018 to 2019 and then sold during 2019? How do I file that?

Ok ... depends on what you mean when you say "transactions"  .... only sales are reported on a tax return no matter when they were purchased ... so pull out the prior year sales from the list given and only report the 2019 sales on the 2019 tax return. 

Ok .. got it! Thanks a lot @Critter