The manual is HERE 

This is what the manual says about memory:

Addressing Memory With 4-GB Configurations

This computer supports a maximum of 4 GB of memory when you use two 2-GB DIMMs. Current operating systems, such as Microsoft® Windows® XP, can only use a maximum of 4 GB of address space; however, the amount of memory available to the operating system is less than 4 GB. Certain components within the computer require address space in the 4-GB range. Any address space reserved for these components cannot be used by computer memory.

If you use a 64-bit operating system, the entire memory range is available to the operating system.

There is nothing in the description of A02 about memory.  It does state adds support for new processor. 

THIS is the Crucial Memory for this model (we suggest Crucial as it is guaranteed to work in Dell's, not all brands will work in all Dell's).

Thanks for the fast answer. Which Memory you can suggest me (other brands)? This Crucial Memory is not available in the local shops in my city.

I have Optiplex 210L with 4 GB RAM (Crucial) BIOS ver A02. A02 does not provide for memory remapping. Is there a newer BIOS upgrade that will allow for my 64 bit OS to see all of the 4 GB RAM?

No you will never be able to use all 4 gigs.  This is a chipset limitation.