How ca i active personal hotspot in my iphone

Are you provisioned by your phone carrier to use hotspot?

understanding hotspot http://support.apple.com/kb/HT4517

Verify that your carrier supports Personal Hotspot for your device and that you have Personal Hotspot enabled on your cellular plan:

From Here > http://support.apple.com/kb/HT3574

Personal Hot spot

Understanding > http://support.apple.com/kb/HT4517

Trouble Shooting > http://support.apple.com/kb/TS2756

iOS- System requirements for Personal Hotspot

iOS- Understanding Personal Hotspot

iOS- Troubleshooting Personal Hotspot