Upgrading from 3.2.1 to 4 - Googlecloud12/Font-Awesome GitHub Wiki
Assets (fonts, stylesheets)
Of course, you need to update the Font Awesome assets, but this is not part of this guide.
New default syntax
icon-*->fa fa-*(Note:fa, base class is only needed by icons),icon-fixed-width->fa-fw,icon-large->fa-lg,icons-ul->fa-ul,icon-li->fa-li,icon-spin->fa-spin,icon-rotate-*->fa-rotate-*.
New icon names
ban-circle->ban,bar-chart->bar-chart-o,beaker->flask,bell->bell-o,bell-alt->bell,bitbucket-sign->bitbucket-square,bookmark-empty->bookmark-o,building->building-o(4.0.2),calendar-empty->calendar-o,check-empty->square-o,check-minus->minus-square-o,check-sign->check-square,check->check-square-o,chevron-sign-down->chevron-down,chevron-sign-left->chevron-left,chevron-sign-right->chevron-right,chevron-sign-up->chevron-up,circle-arrow-down->arrow-circle-down,circle-arrow-left->arrow-circle-left,circle-arrow-right->arrow-circle-right,circle-arrow-up->arrow-circle-up,circle-blank->circle-o,cny->rmb,collapse-alt->minus-square-o,collapse-top->caret-square-o-up,collapse->caret-square-o-down,comment-alt->comment-o,comments-alt->comments-o,copy->files-o,cut->scissors,dashboard->tachometer,double-angle-down->angle-double-down,double-angle-left->angle-double-left,double-angle-right->angle-double-right,double-angle-up->angle-double-up,download->arrow-circle-o-down,download-alt->download,edit-sign->pencil-square,edit->pencil-square-o,ellipsis-horizontal->ellipsis-h(4.0.2),ellipsis-vertical->ellipsis-v(4.0.2),envelope-alt->envelope-o,exclamation-sign->exclamation-circle,expand-alt->plus-square-o(4.0.2),expand->caret-square-o-right,external-link-sign->external-link-square,eye-close->eye-slash,eye-open->eye,facebook-sign->facebook-square,facetime-video->video-camera,file-alt->file-o,file-text-alt->file-text-o,flag-alt->flag-o,folder-close-alt->folder-o,folder-close->folder,folder-open-alt->folder-open-o,food->cutlery,frown->frown-o,fullscreen->arrows-alt(4.0.2),github-sign->github-square,google-plus-sign->google-plus-square,group->users(4.0.2),h-sign->h-square,hand-down->hand-o-down,hand-left->hand-o-left,hand-right->hand-o-right,hand-up->hand-o-up,hdd->hdd-o(4.0.1),heart-empty->heart-o,hospital->hospital-o(4.0.2),indent-left->outdent,indent-right->indent,info-sign->info-circle,keyboard->keyboard-o,legal->gavel,lemon->lemon-o,lightbulb->lightbulb-o,linkedin-sign->linkedin-square,meh->meh-o,microphone-off->microphone-slash,minus-sign-alt->minus-square,minus-sign->minus-circle,mobile-phone->mobile,moon->moon-o,move->arrows(4.0.2),off->power-off,ok-circle->check-circle-o,ok-sign->check-circle,ok->check,paper-clip->paperclip,paste->clipboard,phone-sign->phone-square,picture->picture-o,pinterest-sign->pinterest-square,play-circle->play-circle-o,play-sign->play-circle,plus-sign-alt->plus-square,plus-sign->plus-circle,pushpin->thumb-tack,question-sign->question-circle,remove-circle->times-circle-o,remove-sign->times-circle,remove->times,reorder->bars(4.0.2),resize-full->expand(4.0.2),resize-horizontal->arrows-h(4.0.2),resize-small->compress(4.0.2),resize-vertical->arrows-v(4.0.2),rss-sign->rss-square,save->floppy-o,screenshot->crosshairs,share-alt->share,share-sign->share-square,share->share-square-o,sign-blank->square,signin->sign-in,signout->sign-out,smile->smile-o,sort-by-alphabet-alt->sort-alpha-desc,sort-by-alphabet->sort-alpha-asc,sort-by-attributes-alt->sort-amount-desc,sort-by-attributes->sort-amount-asc,sort-by-order-alt->sort-numeric-desc,sort-by-order->sort-numeric-asc,sort-down->sort-desc,sort-up->sort-asc,stackexchange->stack-overflow,star-empty->star-o,star-half-empty->star-half-o,sun->sun-o,thumbs-down-alt->thumbs-o-down,thumbs-up-alt->thumbs-o-up,time->clock-o,trash->trash-o,tumblr-sign->tumblr-square,twitter-sign->twitter-square,unlink->chain-broken,upload->arrow-circle-o-up,upload-alt->upload,warning-sign->exclamation-triangle,xing-sign->xing-square,youtube-sign->youtube-square,zoom-in->search-plus,zoom-out->search-minus.
Other classes changes
icon-white->fa-inverse,icon-large->fa-lg,icon-2xtoicon-4xreplaced withfa-2xtofa-4xandfa-5xadded.