[sql] Changing the maximum length of a varchar column?

I'm trying to update the length of a varchar column from 255 characters to 500 without losing the contents. I've dropped and re-created tables before but I've never been exposed to the alter statement which is what I believe I need to use to do this. I found the documentation here: ALTER TABLE (Transfact-SQL) however I can't make heads or tails of it.

I have the following so far (essentially nothing unfortunately):

alter table [progennet_dev].PROGEN.LE
alter column UR_VALUE_3

How do I approach this? Is there better documentation for this statement out there (I did some searches for an example statement but came up empty)?

ALTER TABLE TABLE_NAME MODIFY COLUMN_NAME VARCHAR(40);

Late to the question - but I am using Oracle SQL Developer and @anonymous's answer was the closest but kept receiving syntax errors until I edited the query to this.

Hope this helps someone

For MariaDB, use modify column:

ALTER TABLE table_name MODIFY COLUMN column_name VARCHAR (500);

It will work.

Using Maria-DB and DB-Navigator tool inside IntelliJ, MODIFY Column worked for me instead of Alter Column

Increasing column size with ALTER will not lose any data:

alter table [progennet_dev].PROGEN.LE 
    alter column UR_VALUE_3 varchar(500) 

As @Martin points out, remember to explicitly specify NULL | NOT NULL

This worked for me in db2:

alter table "JOBS"  alter column "JOB_TITLE" set  data type varchar(30);

You can use modify:

ALTER TABLE `table name` 
modify COLUMN `column name` varchar("length");

In Oracle SQL Developer

ALTER TABLE car_details MODIFY torque VARCHAR(100);

I was also having above doubt, what worked for me is

ALTER TABLE `your_table` CHANGE `property` `property` 
VARCHAR(whatever_you_want) CHARACTER SET utf8 COLLATE utf8_unicode_ci NOT NULL;  

As an alternative, you can save old data and create a new table with new parameters.

In SQL Server Management Studio: "your database" => task => generatescripts => select specific database object => "your table" => advanced => types of data to script - schema and data => generate

Personally, I did so.