Hi and welcome to Android forums.
First and foremost, is your phone rooted? By your question, i expect the answer to be yes, but worth checking. The reason i say that is that in 99% of cases, you are unable to delete stock apps that came preloaded on the phone OS. This is so that an app is not inadvertently deleted that would adversely disrupt device functionality.
If your phone is rooted then the above statement isn't true as you can delete system apps either by design or by accident. In this situation, the best thing you can do is find out which app it is you deleted and see if you can find somewhere where you can download a replacement (registering here might be a good start, see last paragraph below).
It could just be that if your phone is saying that the update isn't compatible with your phone then it could just be a plain statement that the update
isn't actually compatible with your phone and therefore you shouldn't download it. Don't forget, just because a general software update might be available for your phone, it doesn't mean that your carrier supports it yet. In cases like this, it is better to wait for your carrier to release their official update.
Can you remember what the name of the app you deleted was please? If you can, please submit another question using the guest function, remembering to reference this question and provide any additional information. Alterantively, you could register on the forums using the link in my signature below so we can provide more interactive help with your issue.
I hope this helps
