Need Partitioning Help Please

[JaMa-JoAd]

I brought a Mac Mini last week, and only really had time this weekend to transfer my data from Windows to Mac.
Everything was going OK until now.
It's a 1TB drive, so I partitioned it in to 1 500GB drive, and then 5 seperate 100GB drives (1 for music, 1 for photos etc) and now, after deciding that I will just put it back to 2 500GB I get the following 2 issues:

1) when I delete the data from one of the partitions, and then right-click > get info it still showing i have data used in there when it's actually free.

and

2) when i extend the partition I get:

Partition failed with the error:
Couldn’t modify partition map because file system verification failed.

can anyone help? Never used a mac before

 

[JaMa-JoAd]

Please close this topic. Seem to have fixed it (the part about why it would extend) how i cannot seem to find out why in Disk Utility it still shows data on the disk when there isn't but i'm guessing thats normal?