How to increase memory limit, maximum execution time, maximum input time and maimum post size

Option a

Login to your cpanel >> Go to "Select PHP version"
select php version to 5.3 or whatever version you would like to select from there and click on "Set as current" button
After that, click on "Use Default" button
Now, click on "Switch to PHP Extensions" button and make the changes for post_max_size and then save

Option b

Create a php.ini and place the following code in /public_html and  /administrator and /wp-admin if they do exist

max_execution_time = 300
max_input_time = 300
memory_limit = 500M
post_max_size = 100M
max_input_vars = 5000