Very slow iphone 4 - can anyone help?

[mpandrich]

I got an iPhone 4 for Xmas, which was nice and speedy. However, I recently plugged into my iTunes and it suggested an update. It took 2 hours, and now my whole phone runs ridiculously slow.
It wont load videos on YouTube, iTunes takes 25 mins to download and I can't listen to the preview so can't even hear what the song is like.
Went back to tmobile, they've said they can't help as its an apple problem but their iTunes runs slowly.
Can anyone help? Tia x

 

[bab2010]

factory reset the iPhone again.

 

[mpandrich]

How do I do that? And will I lose my music and contacts?
Meg

 

[bab2010]

connect your iPhone to your computer, open up iTunes and there you will see the option to either check for update or to restore. Click on restore and let iTunes restore your iOS. You can use iCloud to backup your contacts and other files, you also have the option to backup your iPhone using iTunes, however i think doing a backup on iTunes and restoring that backup later will bring back that issue in the phone, so your best option will be to backup your most important files like contacts etc... using iCloud on your iPhone. Good luck.