Converting airtime to mobile data is as simple as buying data with your airtime credit.
The benefit of buying data up front with your airtime credit is that you can get much better value for money. For example, Vodacom will charge you R2 per MegaByte if you have not converted some of of your airtime to data by purchasing a data bundle up front. If you spend as little as R5 of your airtime on a data bundle, then you will get 20 MegaBytes of data which means you are only spending 25c per MegaByte, a much beter deal than R2 per Megabyte. Typically the more you spend on a data bundle the cheaper the data becomes, so the more value you get for your money and similar principles apply for all providers though I have only mentioned Vodacom.
Do bear in mind that once you convert airtime to data, it can no longer be used to make voice calls or send SMS, so ideally you need a bit of data as well as some airtime, depending on your exact needs. The other thing to be aware of is that data expires after 30 days, so don't buy more than you will use in a month or you will end up losing what you don't use.
You can dial the following codes from your handset to buy data bundles or convert airtime to data:
Vodacom: Dial *111#
MTN: Dial *141*6#
CellC: Dial *147#
Telkom Mobile: Dial *180#
... and then follow the prompts (You may notice that some of these USSD codes allow you to manage more than just data bundle purchases).
If you would like a chance to win some airtime that you can convert to data (or use however you please) then enter your number here for a chance to win up to R10 in the daily airtime draw!