Easy. Install imagemagick:

sudo apt install imagemagick

Its simplest usage is:

convert File.tif File.jpg

It is smart and goes by your file extension.

Now, for doing batch conversions, we shall use a loop.

cd into the directory where your tif files are.

then:

for f in *.tif; do  echo "Converting $f"; convert "$f"  "$(basename "$f" .tif).jpg"; done

Read also as:

for f in *.tif

do  

    echo "Converting $f" 

    convert "$f"  "$(basename "$f" .tif).jpg" 

done

That should do it!

Also, once you convert all of the files and verify the new jpg's integrity, just run rm *.tif in that directory to delete all your old .tif files. Be careful with asterisks though, don't add a space after the *, or you will delete all your files in the directory.

Tip: If you have a folder with subfolders that holds these images. You could use this for loop to find all .TIF files within that folder:

for f in $(find -name *.tif); do ...; done