If your iPad 2 is already running iOS 9.3.2 and it is it running OK, you could upgrade to iOS 9.3.5, but at this late stage, I really wouldn't bother.
The BIG reason I wouldn't attempt this update at this late date is older iPad 2 users, lately, have been experiencing this Activation Server Temporarily Unavailable issue that has been problematic to solve and in some cases has bricked the iPad 2.
Not because of the iOS 9.3.5 update, but, I think, has something to do with Apple’s servers not allowing older iPads to no longer upgrade/update to the older iOS any longer and/or could be iPad 2 hardware/battery related issues because these iPad models are 7 years old, now!
After all, iOS 9 is no longer being supported, though lots of app developers are STILL supporting their apps on iOS 9/9.3.5.
I just wouldn't risk this update and risk this Activation Server issues and risk ending up with a bricked iPad for no real reason other than just trying to update this 7 year old iPad to its last and final update!
For future reference there is a way to temporarily remove an iOS upgrade/update so it can't be downloaded at all.
Go into the Settings App, General Settings panel.
In the right hand column, tap Storage and iCloud Usage.
At the top in the first block of 3 panels where it is titled at the top of this block Storage, tap the panel that says Manage Storage.
A list of every app will generate itself.
Once this list stops generating, look through this list until you see something like iOS 9.x.x in this list.
Tap on the gray disclosure arrow at the far right on that iOS 9.x.x panel.
It will bring you to another screen that will allowing you to completely delete/remove the entire iOS upgrade/update. This removal/deletion of an iOS upgrade/update is not permanent and may return at anytime when the iOS upgrade/update at some point will get re-pushed to your iDevice, where you can simply perform this procedure, again.
I STILL use my iPad 2 and 3 models regularly and online with no real issues other than a nearly 2 minute boot up time.
If you want to more effectively use this iPad and use it safely online, again, and speed up its performance some,
Tap on the link below to my iDevice/iOS performance/optimisation user tips link.
https://discussions.apple.com/docs/DOC-10344
Try all of these tips and leave each tip active together. Do not simply try every tip individually, expecting just one tip to be a performance “cure all”.
Many of these tips are designed to work together to improve overall iOS/iDevice performance.
I would STOP using that 2-2-1/2 year old Safari web browser, as it is, probably, not safe and secure to use any longer, and seek out a third party web browser that is STILL currently being updated and STILL being supported on iOS 9.3.5.
Here are a few third party web browsers that I know are STILL being regularly updated and STILL support iOS 9.
Perfect Web browser
iCab Mobile Web browser
Dolphin Web browser
Aloha Web Browser
Maxthon Web browser
Opera Web Browser
Good Luck to You!
