To install Spark, make sure you have Java 8 or higher installed. Then go to Spark Downloads page to select latest spark release, prebuilt package for Hadoop and download it. Unzip the file and move to your /opt (or for that matter any folder, but remember where you moved it)
mv spark-2.4.4-bin-hadoop2.7 /opt/spark-2.4.4
Then create a symbolic link. This way you can download and use multiple spark versions.
ln -s /opt/spark-2.4.4 /opt/spark
Add the following to your, .bash_profile
to tell your bash where to find Spark.
export SPARK_HOME=/opt/spark
export PATH=$SPARK_HOME/bin:$PATH
Finally, to setup Spark to use python3, please add the following to /opt/spark/conf/spark-env.sh file
export PYSPARK_PYTHON=/usr/local/bin/python3
export PYSPARK_DRIVER_PYTHON=python3