Q: my MAC increase memory after I've delete many things!

Is the machine at over 85% capacity?

Is your data backed up?  If not, I recommend getting a 500 GB external hard drive, partitioning it to have 40 GB in one partition, and 420 GB in the second partition.  Install the operating system with Carbon Copy Cloner on the 40 GB partition, and boot off the external drive using the Startup Manager (Option key).   Then run Carbon Copy Cloner to clone the contents of your overflowing Flash drive to the 420 GB second partition.  Both partitions should be Apple HFS Extended Journalled with Options on the Partition GUID.

Once you are backed up, and able to boot off the external 420 GB drive, then you can go about cleaning up the contents of your files.   Note, do not attempt to delete system files.  When you have finally cleaned up all files you no longer will ever need that are not applications, and have at least 50 GB of it freed, then you can clone back to the internal drive the 420 GB drive.

Burn to CD or DVD, or add to a USB Flash drive what you don't need now, but may need later.