I performed it one by one.
7.2.1 to 7.3.0.B1 > Succeeded
7.3.0.B1 to 7.3.0.B2 > Succeeded
7.3.0.B2 to 7.3.0.RC > Succeeded
7.3.0.RC to 7.3.0 > Failed with the following error
Warning: opendir(/home/dolphin/public_html/test/upgrade/files/7.3.0.RC-7.3.0/modules/): failed to open dir: No such file or directory in/home/dolphin/public_html/test/upgrade/classes/BxDolUpgradeUtil.php on line 196
Error reading modules updates.
I checked and found the modules folder was missing. I checked the patched and found it was there. I again extracted the patch but still modules folder was not there... and hence, I manually created the modules folder and successfully upgraded!
Looking for any other error!