Hello ,,
I have OS AIX 5.2 ML 5200-05
Model : 9113-550
we want upgrade 5.2 to 5.3
how I can upgrade 5.2 to 5.3?
I think it has to be done with "smit update_all" command, but I can't be sure, you should contact IBM tech support asking for this. Upgrade of the core OS may be tricky task, depending on your setup and/or installed packages.
Not in case of Version or Release upgrade.
Probably a good idea. 
I'd explore the possibility of an "alternate-disk-installation" or "alternate-disk-migration". You will find a lot of instructions here or spread over the web by entering these words in your favourite search engine.
(like here: pSeries and AIX Information Center)
Basically it works like that: you have a mirrored rootvg, which will be broken into the two parts the mirror consists of, then one of these copies is used to do the upgrade. After everything is proven to be ok the other mirror will be synced, if something fails you can use the untouched copy to step back to where you have started.
I hope this helps.
bakunin