What would be a suitable translation for an update to Facebook or an update to a blog?
Is güncellemek the correct verb?

Fazla zaman için Facebook´ı güncellemdim

I haven´t updated Facebook for too long

´Güncellemek´ is the correct word for ´to update´

so your sentence would be like this :

I haven´t updated Facebook for too long

Facebook´u uzun zamandır güncellemedim.

 I know the Q is about the use of güncellemek, but can I comment on a common English mistake made by Turks: the use of "too".

In this sentence we would say I haven´t updated Facebook for a long time.

In Turkish the word "çok" is used both for "a lot of" and "too much". The difference in English is that in the first one you are just commenting on quantity, without giving an opinion as to whether it is excessive or not. In the second one you are making it clear that a little less would be better.

So Ahmet çok zengin = Ahmet is very rich. Fact

Ahmet is too rich: I think he has more money that he should have.

Facebook´u uzun zamandır güncellemedim. = I haven´t updated facebook for a long time / I haven´t updated facebook in a long while /  or we might even switch it to positive: it has been a long time since I updated Facebook.

If you wanted to say that you should really have updated Facebook a long time ago you would emphasise this as: I haven´t updated facebook for a too long time, but this sounds a bit awkward so we are more likely to use the positive version: It has been too long since I updated Facebook

"I haven´t updated Facebook for too long " Marionin if you look at the original post you will see that this sentence has written by an english person not by a Turk.

English? Turk? Doesn´t matter. My comments are still valid, and hopefully helpful to whoever cares to read them.

 Yes it does matter, since your judgement was about Turks not English.

I know the Q is about the use of güncellemek, but can I comment on a common English mistake made by Turks: the use of "too".

I didn"t say your comments are not valid. I said that mistake has been made by an English not  a Turk. Anyways, thanks for useful information.