I wrote the abstract according to my thesis but realized that it's too much for a conference presentation. Could I use a part of the abstract to present？
I am not quite sure I understand your question ... of course you can present your PhD(?) thesis at a conference and you are also allowed to shorten the abstract in order to fit the conference requirements.
But in general I would rather recommend to re-write the abstract completely because shortened texts tend to be sub-optimal and you might also run into the issue of self-plagiarism if you take (parts of) your abstract with copy&paste.
If by "Could I use a part of the abstract to present" you mean if you could use a part of your ideas/results etc to present then the answer is also yes. There is no rule that you have to present your whole work at once - often it is even better to present one (shorter) clear message at a conference than trying to get the whole thesis into a presentation.
---- EDIT ----
After clarification of the question ("Does it matter if the content of my conference presentation does not (fully) match the abstract that I have submitted?"):
No, it does not matter. Most people will not even realise it. If you like you can say a sentence or two in the beginning that you will focus on a specific sub-part of your abstract (and you are happy to discuss the other aspects during the coffee break etc). But it is up to you!