Plugin update problem

[Moderator Note: Topic title modified. When you start a new topic, use a good topic title. Also, please be aware that your problem is no more urgent than anyone else’s.]

Hello guys, today 1 plugin for share content show me need update, i start update this plugin and i dont get any error but my page refresh alone, and my site now show me onli “Inaccessible due to planned maintenance. Please check back in a minute.” I cant enter in Admin page, i cant enter anywhere? WTF?
How can i fix it? Only this message show me and i cant do nothing. Any help?
Thanks a lot!