Q: My safari is too slow...how to delete and install a fresh safari ?

Safari app is part of the OS so you can't uninstall/install again unless you do a System Restore.

If Safari is too low, erase History, Cookies, Caches, Turn off or delete unwanted Plugins if you have.

If that doesn't help try a deep clean up:

Go to Library > Caches > com.apple.Safari > Caches.db and trash it also

Go to Library > Preferences >  com.apple.Safari.plist and trash it

Reinstalling Safari rarely fixes a, "slow to boot" issue. And reinstalling Safafari on a Mac running Yosemite v10.10 requires restoring OS X using OS X Recovery.

Safari extensions and third party plug-ins are usually the culprit when you have problems with Safari.

So follow the troubleshooting help in this support article >  If Safari is slow, stops responding, quits unexpectedly, or has other issues - Apple Support