This is a server issue. So you should contact your hosting provider. They can increase the php memory limit for you.
Quick fix for Theme packages
1- Unzip the theme package
2- You will see a “documentation” folder. Remove it from the folder (It is help documentation.)
3- Zip the package again and upload it to your wp website via admin panel
Documentation folder is 4-5 mb. So if you remove that folder from the theme package, you will most likely upload the theme without any problem.
Note: After this change, you can’t access to the help documentation from theme settings. You can open it (documentation folder) on your computer with clicking index.html file…