Q: how can i update my browser if i dont have enough memory

What do you mean? Please provide a clearer explanation. See Writing an effective Apple Support Communities question.

You cannot upgrade Safari unless you upgrade OS X. By "memory" do you mean space on the drive? If so, then see:

How to Free Up Space on The Hard Drive

1. You can remove data from your Home folder except for the /Home/Library/ folder.
2. Visit The XLab FAQs and read the FAQ on freeing up space on your hard drive.
3. Also, see Freeing space on your Mac OS X startup disk.
4. See Where did my Disk Space go?.
5. Be sure to Empty the Trash to recover the space.
6. Replace the drive with a larger one. Check out OWC for drives, tutorials, and toolkits.
7. Use OmniDiskSweeper or GrandPerspective to search your drive for large files and where they are located.

It's not just a matter of memory.

See Hardware Requirements for the latest macOS Sierra >  http://www.apple.com/macos/how-to-upgrade/#hardware-requirements