Importing takes time and fails!

Hello
I have a lot of products on my website. Something like 50 thousands. Even when i try to import 2000 products the export/import tool continue to upload for long time then it fails. It takes something like 40 min and it fails.
Do i need to increse the hosting memory or speed?
Why is this happening? Is this tool limited for specific number of products or file weight?

The file is less than 8m.

I wanted to split the excel file to groups, in order to upload 1000 products each time, but the tool deletes previous upload. Is there a way to upload without deleting the existing file?
I hope you can help me because i am looking for solution almost for 2 weeks.
Thank you

If you mean JNeuhoff's free export/import tool, it does not yet do incremental uploads, and it needs elevated php.ini values (as shown).

For the sake of the tool and generally, you can use these settings in your php.ini pair, and in your host control panel if those are fully or partially ignored (as on some servers, outright or just some settings such as memory-limit):

memory_limit = 512M;
max_execution_time = 300;
post_max_size = 999M;
upload_max_filesize = 998M;

Note that post exceeds upload, that is required. Note that mem is in base 2 (binary progression).

Try phpinfo.php to see what the server thinks is going on. The tiny one-line utility phpinfo.php (here: http://forum.opencart.com/download/file.php?id=18153) can be uploaded into OC (or your account, public) and addressed in the browser. Put it in both your OC root and your /admin/. Address it as usual, but after domain/whatever/phpinfo.php (and domain/whatever/admin/phpinfo.php).