1. Unzip the file you downloaded from codecanyon. then you will see the next files (documentation and zigaform-wp-estimator.zip)
   
2. Logging into wordpress, go to Plugins menu on sidebar and press Add new button
   
3. Upload the zigaform-wp-estimator.zip file ( Do not upload whole folder you download from Codecanyon ) and install
4. Install & Activate Zigaform Cost Estimator
   
5. that’s all

NOTE: this zip file is a large file. Most hostings will fail at uploading because there is not enough memory. All you need to do is create a php.ini file and upload it into your /wp-admin folder. Then add the following:
memory_limit = 32M
upload_max_filesize = 32M
post_max_size = 32M
file_uploads = On

if the problem, try using method 2 via ftp

Here a tutorial video: