I assume by safe you mean "stable". If you want to be ultimately safe, don't overclock at all. But if you are looking for a stable overclock, then you will have to test it.
 
Each card, even if the same brand and model, overclocks differently. The easiest way to start is to increase the clock by 5Mhz. There a lot of methods for seeing if you're stable, like benchmarking, burn-in tools, and stress tests. These are good once you find a clock speed that doesn't give you any weird problems after a few minutes.
 
What I recommend is to do a Google search for your card and recorded overclocks. I usually do this to get a feel as to what I can attempt to do.

Here is an article all about your card and you can see what performance increases you could achieve.
 
If you are new to this, then don't look into overvolting as this has the greatest potential to kill your card if you don't do this properly. The only time you really need to do this is after you find a stable overclock and want to push it a bit further.

I do recommend undervolting as you can save power and thus the life of your card for a bit longer. While you should know overclocking will do the opposite. However, you can apply undervolting and overclocking to balance out the two if you want.

As for a program, EVGA Precision is great. I use that but prefer MSI Afterburner.

You can just type in "Afterburner Download" in Google and find it from the MSI page. You don't need one of their products to obtain it.
 
Again, just go through a couple of overclocking reviews for your card as I'm sure they will all get different results. I would then see which review/thread/article had the lowest overclock and aim for that first. If you make that, then you could shoot for something higher.

Just to a little insight to my experiences with my 460. I bought a Geforce 460 SuperClocked 2 years ago, and it is overclocked for almost all of the time it is being used. I use EVGA Precision X which i find to be a really good program. Ill give you some numbers I have gotten.
 
Under stock power settings I can get my core clock to hit 800 mhz  
Stable 
 
With 1000mV I can get the core clock to 850
Stable
 
With max voltage which im sure is a terrible idea i can get it to 925 mhz and it tends to work for an hour or two but then crashes
Unstable/Unsafe (I think)
 
 

I really DO APPRECIATE ALL THE INFO GUYS. I've got A Lot of Playing Around now to do & NOW HAVE SOME GREAT STARTING Points THANKS TO U ALL!!!!
Sincerely,
TWMEANS1/AWMEANS

Carlitos714

Only thing to watch out for are temps. I wouldn't go over 90c, but I really doubt you will see those temps with manual fan control. Let's us know or max over clock!

 
I agree with Carlitos as I won't let my cards go over 90c and Don't want force my babe cards lol!! Do not need put too much overclock and voltage it will no good!! 

In your case if you feel confident and know what you're doing I'd replace the TIM.
 

antjar

Anytime my card gets anywhere near >70 it crashes lol so I haven't even heard of above 90 with my 460.

If you don't feel confident replacing your TIM don't do it. Over a long period of time the TIM can start to dry out so a nice fresh coating can really make a difference.
 

antjar

rjohnson11

In your case if you feel confident and know what you're doing I'd replace the TIM.

antjar

Anytime my card gets anywhere near >70 it crashes lol so I haven't even heard of above 90 with my 460.

Don't know how to do that, but its really not a problem my card hovers at 65 when im oced to my stable oc so it doesn't really matter, also im under warranty so if it became a problem I would just RMA it.

today my GTX 460 v2 sc coming .
My new GTX 1060  sc is not support SLI  .Nvidia let me disappointed .but I collect used GTX 460 .sell send me a GTX 460 v2 .I don't know gtx 460 v2 top Core Mhz