What you have is SRAM's version of the Hollowtech II cranks with the actual bottom bracket fused with the bike in the form of BB30 variant.
You leave the BB alone and by loosening the L crank bolts the L crank will come off. Take a look at parktool.com under the repair section
if looking up S300 cranks on sram.com tech docs doesn't do it. Once the L crank is off you just gently tap or push on the end of the axle
and it will slide out to the R side of the bike. Axle is swedged into the R crank and is unitary with the R crank. The bearings are replaceable
but are a press fit into the frame, unlike the external bearings used with hollowtech variants. This was popular for awhile but less so now than then.
Bearing removal is not hard, but not easy either. They can be gently tapped out from the inside and pressed back in to replace.
The bearings themselves will have numbers/letters on the seal which can be used to buy new. They are standard bearings, not bike specific
and readily available from bearing supply houses. Bearings "should" last for years but YMWV. For some reason the relevant SRAM.com pdf
won't load past p9, so some others will have to supply exact details.

Here is the parktool crankset site, scroll down for SRAM/Truvative, but it does not address your BB30. http://www.parktool.com/blog/repair-...o-ultra-torque

BB at Parktool: http://www.parktool.com/blog/repair-...ottom-brackets