What do you mean side-by-side? Is your system a dual-boot system, so on boot-up you have a choice as to which operating system you run, or is Ubuntu run as a virtual machine inside Windows 7?
Assuming you have a dual-boot system, where Windows 7 and Ubuntu are installed on different disks or partitions, then you should be able to boot from a Red Hat install disk and just install Red Hat Linux onto the disk or partition that currently holds Ubuntu. You would in effect be replacing Ubuntu by installing Red Hat on the same disk/partition as Ubuntu, thereby wiping out Ubuntu with Red Hat.