MongoDB Sharded Cluster Upgrade from 2.4 to 3.2 version
Yes. Period. No "Ok, but..."
You should make a backup. Start now, continue reading later. It is presumably going to take a while.
Config servers in 2.4, 2.6 and 3.0 do *not* form a replica set. Those were basically 3 standalone instances.
Read and understand the migration guide to 2.6 for sharded clusters. Rinse, repeat.
Read and understand the migration guide to 3.0 for sharded clusters. Rinse, repeat.
Read and understand the migration guide to 3.2 for sharded clusters Rinse, repeat.
Read the guide Upgrade Config Servers to Replica Set. Rinse, repeat.
Wait until your backup is done.
Upgrade to 2.6 according to guide mentioned above. Make sure (aka "test thoroughly") your cluster works as expected. Continue at the next appropriate maintenance window.
Upgrade to 3.0 according to the guide mentioned above. Migrate to WiredTiger in the process, unless you have very strange requirements. That is: shutdown data secondary data bearing node, delete its datadir, adjust config to utilize WT, resync, proceed. Have primary step down Before shut down. Make sure (aka "test thoroughly") your cluster works as expected. Continue at the next appropriate maintenance window.
Upgrade to 3.2 according to the guide mentioned above. Make sure (aka "test thoroughly") your cluster works as expected. Continue at the next appropriate maintenance window.
Convert your config servers to a replica set according to the guide mentioned above. Make sure (aka "test thoroughly") your cluster works as expected. Continue at the next appropriate maintenance window.
Take a few notes: "Good resolution 1: read release notes and docs of my chosen persistence technology. Good resolution  2: I will only ask questions to my peers after thoroughly researching the topic myself."