I can't update software ISO 13 in my iPad please help me.

It might be a model that cannot support more recent iOS/iPadOS versions because of hardware (CPU/RAM) incompatibility. Start identifiying your iPad model:--> Identify your iPad model - Apple Support

Then take a look at this list for compatibility:

A little hard to help you when you provide NO information about your iPad.

Your iPad year and model maybe too old for anymore iOS upgrades/updates.

Here are my questions to you.

What year and model iPad do you have/own?

The “A” model number can be found on the aluminium back of your iPad, in small print, right under the larger bold print “iPad”.

What iOS/iPadOS version is this iPad, currently, running?

What is the rated, internal data storage space/capacity of your iPad model and how much of this free, internal data storage capacity is left inside of your iPad model?

All of that additional info can be found in the Settings app, General settings panel, About.

Please attempt to answer all questions asked.

Thank You.