Install sage in Ubuntu

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I have downloaded new version. But if I try like this, it shows much older version. How to fix this?

/sage-9.3-Ubuntu_20.04-x86_64/SageMath$
sage
┌────────────────────────────────────────────────────────────────────┐
│ SageMath version 8.1, Release Date: 2017-12-07                     │
│ Type "notebook()" for the browser-based notebook interface.        │
│ Type "help()" for help.

If I use this, I get following:

sage-9.3-Ubuntu_20.04-x86_64/SageMath$ ./sage
python3: /lib/x86_64-linux-gnu/libm.so.6: version `GLIBC_2.29' not found
(required by
/home/santanu/sage-9.3-Ubuntu_20.04-x86_64/SageMath/local/lib/libpython3.9.so.1.0)
python3: /lib/x86_64-linux-gnu/libc.so.6: version `GLIBC_2.28' not found
(required by
/home/santanu/sage-9.3-Ubuntu_20.04-x86_64/SageMath/local/lib/libpython3.9.so.1.0)