How to parallelize an RDD?

Resilient Distributed Datasets (RDDs) RDD as the name suggests are distributed and fault-tolerant and parallel.

"RDDs are fault-tolerant, parallel data structures that let users explicitly persist intermediate results in memory, control their partitioning to optimize data placement, and ma- nipulate them using a rich set of operators." Please see this paper.

No you don't need to convert an RDD to a Seq object. All processing on RDDs are done in parallel (depending on how parallel your Spark installation is).