When Apple Inc. (NASDAQ:AAPL) rolled out iOS 7 on Wednesday, the company was sending the biggest update to the operating system since it was first introduced. Unfortunately though, the transition has not gone smoothly for millions of Apple users.

apple ios 7

iOS 7 downloaders take to Twitter

Numerous Apple users who have already downloaded iOS 7 have gone on Twitter complaining about the update. Long download times were a problem for some, while others reported having to try multiple times just to install the updated operating system. Still others reported that they had deleted all of their pictures, music and apps but still didn’t have enough room on the device to actually download iOS 7.

NBC News’ Wilson Rothman reported Wednesday evening that they had updated an iPhone 5, but it was “acting funny” after the update. According to Rothman, it was powering down occasionally and showing that the battery was either low or at zero.

The few who were actually able to download and install iOS 7 on their devices though, did have good things to say about it.

What happened to iOS 7?

Sophie Curtis of The Telegraph reports that problems with Apple Inc. (NASDAQ:AAPL)’s servers could be the source of the issues. The company may simply not have been ready for the surge in traffic as users around the world attempted to download and install iOS 7—all at the same time. However, a check of Apple’s System Status page does not indicate any problems. All services are said to be up and running according to the page.

CNET’s Josh Lowensohn reports that the iOS 7 download is bigger than most of the other over-the-air updates Apple Inc. (NASDAQ:AAPL) has released in the past. The version for older iOS devices can be 600 MB, although the version for newer devices appears to be as large as 935 MB in size. In some cases, the update appears to be as large as 3 GB.

CNET also reported that some users reported problems with Apple’s activation servers, although it is unclear how many users are having these problems.