I am having Tenda N301 Router having 2 antenas. I want to load OpenWrt Image in it so i can use OpenWrt's advanced features. Can please anyone help me out for it?
No one can help you I'm afraid. This is a device that is very much past end of life (dates back to 2013) as it has only 16MB ram and 2 MB flash (as well as a Broadcom SoC). OpenWrt would not come anywhere close to fitting on the flash to start with.
If it works well enough for you as it is then fine but otherwise consider purchasing an up to date device. ~$20 should get you something with 16MB flash and 128 MB ram and a much better/supportable SoC.