hozansahin go to installed Roundcube Directory and open UPGRADING Docs, and follow the instructions in this document, that's how I updated. sorry for my english, i'm from turkey 🙂
mousehole check if lsphp74-intl.x86_64 0:7.4.28-1.el7 is installed. In my case this solved my problem. An easy way to find what's going wrong is to look into /www/wwwroot/webmailaddress.yourdomain.xxx/logs/error.log