I'm running this ram hynix 512mb 2rx16 pc2-5300s-555-12 hymp564s64cp6-y5 ab can I replace it with a 2Rx8 in other to upgrade my speed

What model do you have? To find the model identifier open System Profiler in the Utilities' folder. It's displayed in the panel on the right. You may also find the complete model information by selecting About This Mac from the Apple menu.

The only version of OS X to which you can upgrade is 10.7.5.

Upgrading to Lion

You can purchase Lion at the Online Apple Store. The cost is $19.99 (as it was before) plus tax. It's a download. You will get an email containing a redemption code that you then use at the Mac App Store to download Lion. Save a copy of that installer to your Downloads folder because the installer deletes itself at the end of the installation.

Lion System Requirements

1. Mac computer with an Intel Core 2 Duo, Core i3, Core i5, Core i7,

or Xeon processor

2. 2GB of memory

3. OS X v10.6.6 or later (v10.6.8 recommended)

4. 7GB of available space

5. Some features require an Apple ID; terms apply.

Are my applications compatible? See App Compatibility Table - RoaringApps.

No matter what memory you install the memory speed remains the same because it is determined by the computer bus not the rated speed of the memory.

Yes. To install the max. you can use one 4GB piece and a 2GB piece or two 4GB pieces (but the computer will only recognize 2GBs.)

Afraid so. It's a matter of your hardware, not the RAM.

Glad to help. Have a great day. 😀