htc m7 can't update it to lollipop Whenever I try to download my software update. The download completes but at the end it gives a notification that my phone has already been modified. I don't know what it is but I can't update my phone's software. HELP ME WITH IT...
Did you root your phone or have you installed custom recovery and such on it? Like the notification says, it throws such errors when the phone is detected to have been modified.

If you really haven't touched the phone in aforementioned ways, then you might have to resort to manually upgrading by using OTA zips, which has some prerequisites and is more complicated to do.