resize /tmp partition

[tolis]

Hi to everyone
Since yesterday i ran into this problem: When i execute a mysql query resulting to more than 30000 results rows, i get in my webpage this error:
Error writing file '/tmp/MYzxhmFg' (Errcode: 28)

After asking a 4PSA tech he advised me to indrease size in /tmp partition.

Any ideas on how to(i have only ssh access to the server)?

Thanks