i have an old mac but unable to use it due to updte requirements

Without knowing which model & year Mac you have it's impossible to say whether yours can be updated or not. However, any Mac old enough to run Mac OS X 10.5.8 Leopard will not be able to be upgraded to anything particularly useful.

Which model & year Mac do you have?

There are literally hundreds of different Mac models.

Find your Mac model name and serial number - Apple Support

Ideally, determine its Model Identifier. It is a text string containing no spaces, resembling the example in that screenshot: MacBookPro18,2

Please do not post its serial number.