Hello and welcome to Apple Support Communities:
The Yosemite OS X 10.10 is no longer available for download from
the Mac App Store; the OS X new version there is El Capitan 10.11.
{Any downloads offered online would be suspect at this point in time if
you wanted Yosemite. Other downloads shouldn't be used for software;
questionable third-party softonic, and other odd sites; avoid bittorents.}
While El Capitan should run in your older MacBook 13-in Late 2009
adequately, it may seem slower than Snow Leopard 10.6.8 with 4GB
RAM and whatever size rotational hard drive storage capacity exists.
The older applications likely would require a newer version upgrade
if you have any third party apps or utilities. Other than web browsers
is there a pressing need to get an entirely new OS X system now?
(You also should know the replacement for iPhoto, is Photos. It is a
bit different and has various changes over older iPhotos. For some
this has been an issue. Also support for older iDevices may not go
well with the latest OS X in a Mac, if the old iPod, etc cannot run a
later iOS to sync; or cannot be seen in a newer iTunes Store, etc.)
The Firefox browser is supportive of OS X 10.6.8 Snow Leopard.
Safari has not been upgraded for Snow Leopard for years. Cannot
say about Chrome; it likely would be a drag on system resources in
that computer configuration with any OS X version.
• How to Download and Install Firefox on Mac - Firefox help:
https://support.mozilla.org/en-US/kb/how-download-and-install-firefox-mac
So I suggest Firefox, as it is a modern browser that supports HTML5
and other features, has maker created modifications you can add,
seems to work fine for many users, and does not need a new OS X.
To upgrade from OS X 10.6.8 to OS X 10.11.3 would bring along with it
many out-dated system parts that would need to be weeded out...
Other options may exist, such as upgrade to Mountain Lion 10.8.5 which
would be a purchase in the Apple Store online, with a download code sent
to your email, that unlocks the download of the OS X from the App Store.
The look and feel of El Capitan is different than older OS X versions. But
not too much. The Mountain Lion purchase would be about $20. USD.
The computer you have could use a memory chip upgrade to 8GB total,
and perhaps the old hard drive may be getting tired. At best consider the
MacBook you have could use a few replacement parts before new OS X.
Good luck in your choices! 🙂
