Unable to select demo theme

I am getting the following error when I try to customise the Highend theme. I have installed it and cant seem to do anything at all. I need the photographic template and that wont download – telling me I have to change all thee settings in files I cant even find. Please help. Im no idiot but i need some comprehensive instructions.

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Please resolve these issues with your server configuration before importing any demo template:

Maximum Execution Time (max_execution_time) : 120 seconds. Recommended max_execution_time should be at least 400 Seconds.
Maximum Input Time (max_input_time) : 60 seconds. max_input_time should be at least 300 Seconds.
WordPress Memory Limit (WP_MEMORY_LIMIT) : 40M memory limit should be at least 64MB. Please refer to : Increasing memory allocated to PHP for more information

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Internal Server Error

The server encountered an internal error or misconfiguration and was unable to complete your request.

Please contact the server administrator, and inform them of the time the error occurred, and anything you might have done that may have caused the error.

More information about this error may be available in the server error log.