No, it is not available online. You need to purchase the upgrade to win98 (I
suggest win98SE)

It is available for purchase on ebay.

Be careful because there are several version available:

1. Update - This one requires that win98 be installed and will upgrade a
win98 installation to win98SE. Microsoft once sold this for 19.95 + Shipping
and handling. I have seen it on ebay for $25-30.
Note: This cannot be used for a clean install and cannot be used to upgrade
from win95.

2. Retail Upgrade version . This one can be used to upgrade or for a clean
install (requires proof of qualifying product for clean install.

3. Retail Full version - This can be used for upgrade or
clean install (normally the most expensive)

4. OEM version - This version was designed for a clean install and my not
allow an upgrade. Normally the most available version