Well, you should increae its size, but how depends on how /tmp was created initially. A couple of possible ways if it's a real partition:
1. Add a new disk and add a larger /tmp partition to that and use that in fstab instead of the current one
2. Backup, repartition and restore
3. Remove the current /tmp partition from fstab umount it and create a larger one by modifying /scripts/securetmp and increasing the default size from 512000 to 1024000
If it was created as a virtual partition to begin with you'll need to umount /tmp (after closing all access processes) delete the existing one and do step 3 above.
If you don't understand any of the above, you'll need to get yourself a server admin to help.